Wiring board sheet and its manufacturing method, multilayer board and its manufacturing method

ABSTRACT

A wiring board sheet which enables the miniaturization of a wiring board by mounting electric components ( 10 ) in an insulation layer ( 4 ) to increase the quantity of mounting electric components, has a high reliability, and undergoes a complicated manufacturing process, and a method for manufacturing the wiring board sheet A multilayer board which is mannufactured from this wiring board sheet, eliminates a difference in thermal histories during molding in each layer, simplifies the manufacturing process, and realize miniaturization by the scale-down and high-density of a conductor circuit and an improvement in reliability, and a method for manufacturing the multilayer board.

TECHNICAL FIELD

The present invention relates to a wiring board sheet used for themanufacture of a wiring board and its manufacturing method, as well asto a multilayer board manufactured from such a wiring board sheet andits manufacturing method.

BACKGROUND TECHNOLOGY

In recent years, an increase in the integration of semiconductors,reduction in the distance of the wires and miniaturization of printedwiring boards have been required in accordance with demands for thedevelopment of the functions, miniaturization and reduction of thethickness of electronic apparatuses. Semiconductor devices and electriccomponents in chip form such as bare chips, capacitors in chip form andinductors in chip form are mounted on such a printed wiring board.

However, such electric components are mounted only on conductor circuitson the external layers of a printed wiring board, and therefore, thequantity of electric components which are mounted on the printed wiringboard is limited while such electric components are placed so as toprotrude from the external surfaces of the printed wiring board, whichhinders the miniaturization of the printed wiring board. In addition, inthe case where electric components are mounted on positions of theoutermost layers of a wiring board, freedom in the wiring design isrestricted.

These problems become more significant as a greater number of layers areincluded in a printed wiring board. That is to say, the greater thenumber of layers included in a printed wiring board, the greater thequantity of wiring, while electric components are mounted solely on theexternal layers of the printed wiring board resulting in the reductionof the quantity of electric components mounted on the printed wiringboard relative to the quantity of wiring, and therefore, theminiaturization of a printed wiring board due to an increase in thenumber of layers is limited by the quantity of electric componentsmounted on the printed wiring board.

In addition, as disclosed in Japanese Unexamined Patent PublicationH11(1999)-126978, manufacture of a multi-layered wiring board has beenproposed wherein an air space is provided in an insulation layer so thatsemiconductor elements and the like are mounted in this air space, andfurthermore, such insulation layers made of photosensitive resin andwired circuits are sequentially layered so as to form the wiring boardaccording to the prior art. According to this technology, it becomespossible to mount electric components within insulation layers so thatan increase in the quantity of mounted electric components,miniaturization of a wiring board and an increase in the freedom ofwiring are achieved to some extent while air is sealed in a gap that hasoccurred between the inner surface of an air space and an electriccomponent, causing a high risk of a crack in an insulation layer and adefect due to damage of or disconnection of the wire of an electriccomponent to occur as a result of a thermal expansion of air within theair space in the case where the wiring board is subjected to stress dueto heat, and in addition, the manufacturing process for such a wiringboard becomes complicated because an air space must be created in aninsulation layer in accordance with the dimensions or the quantity ofthe mounted electric components. In addition, insulation layers andconductor circuits are sequentially layered to form a multilayer boardin the case of fabrication of a multilayer board, and therefore, theformation of an insulation layer and the formation of a conductorcircuit need to be repeated alternately, requiring time and effort forvery complicated procedure in the manufacture of the multilayer board.In addition, a heat treatment is required for the curing to form aninsulation layer whenever one layer of an insulation layer or conductorcircuit is formed, and therefore, each conductor circuit formed in eachlayer has a different thermal history leading to a different contractionratio of each conductor circuit pattern, which requires correction. Inaddition, at the time of the formation of an insulation layer on aconductor circuit pattern, a conductor circuit is buried in aninsulation layer as a result of the curing of an insulating resin thathas been melted for the formation of the insulation layer whereinunevenness in the wiring board that occurs when a conductor circuit isburied in an insulation layer becomes greater as a greater number oflayers are included in the wiring board. In some cases, the unevennessin the wiring board causes a failure in the formation of an insulationlayer that covers unevenness of a conductor circuit in a manner where anextremely thin portion is formed in the insulation layer causing a highrisk of lowering the reliability of the insulation.

Furthermore, connection structures such as pad on via and via on via cannot be formed according to such a conventional manufacturing method, anda problem arises wherein there is a limit in the increase in the densityof the conductive circuit, and there is a limit in the reduction of theboard area, preventing the reduction in the distance of signal paths.

In addition, a component is inserted in an insulation layer, andthereby, the length of a via in this insulation layer becomes extremelylarge, causing a big problem in the reliability of the conductiveresistance of the via.

As described above, several problems exist in the conventionalmanufacturing method concerning the reduction of unevenness of a circuitlayer by efficiently burying components in the layer as well asconcerning the securing of connection reliability, and the quantity ofmounting when components are mounted.

The present invention is provided in view of the above describedproblems, and an object thereof is to provide a wiring board sheet witha high reliability, as well as its manufacturing method, that allowsminiaturization of a wiring board where electric components are mountedwithin an insulation layer, and thereby, the quantity of electriccomponents to be mounted is increased and that allows a manufacture of awiring board without undergoing a complicated manufacturing process andto provide a multilayer board with an increased reliability, as well asits manufacturing method, that allows miniaturization of a wiring boardwhere electric components are mounted within an insulation layer, andthereby, the quantity of electric components to be mounted is increased;that allows the formation of multiple layers in a collective mannerresolving a problem caused by a difference in the thermal histories ofthe respective layers at the time of formation and allowing for thesimplification the manufacturing process; and that allowsminiaturization of the wiring board as a result of scale-down anddensity-increased conductive circuits, achieving an increase in thereliability.

DISCLOSURE OF THE INVENTION

A manufacturing method for a wiring board sheet according to the presentinvention is characterized in that: a base 6 for transcription, on asurface of which a conductor circuit 5 is placed and an electriccomponent 10 is mounted or is formed through printing on this conductorcircuit 5, is layered on one or two surfaces of a resin layer 4 in theB-stage so that the conductor circuit 5 as well as the electriccomponent 10 and the resin layer 4 are opposite to each other; theconductor circuit 5 and the electric component 10 are buried in theresin layer 4; and the base 6 for transcription is released from theresin layer 4 while the conductor circuit 5 is made to remain on theresin layer 4 side, resulting in the transcription of the conductorcircuit 5 to the resin layer 4, so that the external surface of theresin layer 4 and the exposed surface of the conductor circuit 5 are inthe same plane when a wiring board sheet is formed.

In addition, a manufacturing method for a wiring board sheet accordingto the present invention is characterized in that: in the abovedescribed manufacturing method for a wiring board sheet, the conductorcircuit 5 is transcribed to only one surface of the resin layer 4 byusing the base 6 for transcription so that the external surface of theresin layer 4 and the exposed surface of the conductor circuit 5 are inthe same plane when a wiring board sheet is formed; and a metal foil 9or a metal foil 17 with resin is layered on and integrated with theother surface of the resin layer 4.

In addition, a manufacturing method for a wiring board sheet accordingto the present invention is characterized in that: in the abovedescribed manufacturing method for a wiring board sheet, the conductorcircuit 5 is placed on a surface of the base 6 for transcription, onwhich the electric component 10 is mounted, wherein a stainless steelbase is used as the base 6 for transcription; the conductor circuit 5 isformed by carrying out a plating treatment after the formation of aresist on the surface of the base 6 for transcription; the electriccomponent 10 is mounted or is formed through printing; and underfill isused on the mounting surface side of the electric component 10.

In addition, a manufacturing method for a wiring board sheet accordingto the present invention is characterized in that: in the abovedescribed manufacturing method for a wiring board sheet, a protectivefilm 12 is layered on one or two surfaces of the resin layer 4 after theconductor circuit 5 has been transcribed; a through hole 3 is created soas to penetrate the resin layer 4, the conductor circuit 5 and theprotective film 12; a conductive paste 8 is applied to the externalsurface side of the protective film 12 so that the through hole 3 isfilled in with conductive paste 8; and after that, the protective film12 is released from the resin layer 4 so that the conductive paste 8protrudes from the through hole 3 towards the outside when a wiringboard sheet is formed.

In addition, the manufacturing method for a wiring board sheet accordingto the present invention is characterized in that: a metal foil 9 islayered on and integrated with the surface, on the opposite side of thesurface on which the conductor circuit 5 has been formed, of the wiringboard sheet 1 on only one surface of which the conductor circuit hasbeen formed according to the above described manufacturing method for awiring board sheet, or a base for transcription on which a circuit isplaced is layered on and integrated with the surface, on the oppositeside of the surface on which the conductor circuit 5 has been formed, ofwiring board sheet 1 on only one surface of which the conductor circuithas been formed according to the above described manufacturing methodfor a wiring board sheet in a manner where the conductor circuit and theresin layer are opposite to each other.

In addition, the manufacturing method for a wiring board sheet accordingto the present invention is characterized in that: the protective film12 is layered on one or two surfaces of the resin layer 4 after theconductor circuit 5 has been transcribed to one or two surfaces of theresin layer 4; the through hole 3 is created so as to penetrate theresin layer 4, the conductor circuit 5 and the protective film 12; ahole plating 18 is provided on the inner surface of the through hole 3;a resin paste 20, or the conductive paste 8, is applied to the externalsurface side of the protective film 12 so that the through hole 3 isfilled in with the resin paste 20, or the conductive paste 8; and afterthat, the protective film 12 is released from the resin layer 4.

In addition, a manufacturing method for a wiring board sheet accordingto the present invention is characterized in that: in the abovedescribed manufacturing method for a wiring board sheet, a stainlesssteel base having a thickness of from 50 μm to 150 μm on which a surfaceroughening treatment has been carried out so that the degree of surfaceroughness, Ra, of the surface on which the conductor circuit 5 isformed, becomes 2 μm or less, is used as the base 6 for transcription.

In addition, a manufacturing method for a wiring board sheet accordingto the present invention is characterized in that: in the abovedescribed manufacturing method for a wiring board sheet, the resin layer4 is formed of a resin composition that contains at least one type ofinorganic fillers selected from among silica, alumina, aluminum nitride,boron nitride, titanium oxide, aluminum borate and magnesium oxide wherethe maximum grain diameter of these inorganic fillers is 10 μm or less.

In addition, a manufacturing method for a wiring board sheet accordingto the present invention is characterized in that: in the abovedescribed manufacturing method for a wiring board sheet, the resin layer4 is formed of a resin composition of which the content of the inorganicfiller is from 70 wt. % to 95 wt. % and that contains at least either acoupling agent or a dispersing agent.

In addition, a manufacturing method for a wiring board sheet accordingto the present invention is characterized in that: in the abovedescribed manufacturing method for a wiring board sheet, the resin layer4 is formed of a resin sheet 4 a gained by impregnating an unwoven clothwith a resin composition which is then dried.

In addition, a manufacturing method for a wiring board sheet accordingto the present invention is characterized in that: in the abovedescribed manufacturing method for a wiring board sheet, after theformation of the resin layer 4, the resin layer 4 is maintained in theB-stage.

A wiring board sheet according to the present invention is characterizedby being manufactured in accordance with the above describedmanufacturing method for a wiring board sheet.

A manufacturing method for a multilayer board according to the presentinvention is characterized in that a plurality of wiring board sheetseach of which is the same as the above described wiring board sheet 1are layered and integrated so as to form a multilayer board.

In addition, the manufacturing method for a multilayer board accordingto the present invention is characterized in that at least one wiringboard sheet 1 from among the above described wiring board sheets and atleast one sheet 13, which has the resin layer 4 in the B and/or C-stageand of which the inside the electric component 10 is not buried, arelayered to be integrated so as to form a multilayer board.

In addition, a manufacturing method for a multilayer board according tothe present invention is characterized in that, in the above describedmanufacturing method for a multilayer board, at least one wiring boardsheet 1 from among the above described wiring board sheets and at leastone sheet 13, which has the resin layer 4 in the B and/or C-stage and ofwhich the inside the electric component 10 is not buried, are layeredand then are collectively molded in this condition to become amultilayer board.

In addition, a manufacturing method for a multilayer board according tothe present invention is characterized in that, in the above describedmanufacturing method for a multilayer board, at least one wiring boardsheet 1 from among the above described wiring board sheets is used inlayering and via hole creating processes according to a build-upmanufacturing method.

In addition, a manufacturing method for a multilayer board according tothe present invention is characterized in that: in the above describedmanufacturing method for a multilayer board, a through hole 19 iscreated so as to penetrate the layered body after the layering andintegrating process; hole plating 18 is provided on the inner surface ofthe through hole 19; and after that, this through hole 19 is filled inwith the resin paste 20 or the conductive paste 8.

Furthermore, a multilayer board according to the present invention ischaracterized by being manufactured according to the above describedmanufacturing method for a multilayer board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a) to 1(c) are cross sectional views showing an example of amanufacturing process for a wiring board sheet;

FIGS. 2( a) to 2(c) are cross sectional views showing another example ofa manufacturing process for a wiring board sheet;

FIGS. 3( a) to 3(d) are cross sectional views showing another example ofa manufacturing process for a wiring board sheet;

FIGS. 4( a) to 4(c) are cross sectional views showing still anotherexample of a manufacturing process for a wiring board sheet;

FIGS. 5( a) to 5(d) are cross sectional views showing still anotherexample of a manufacturing process for a wiring board sheet;

FIGS. 6( a) and 6(b) are cross sectional views showing still anotherexample of a manufacturing process for a wiring board sheet;

FIGS. 7( a) and 7(b) are cross sectional views showing still anotherexample of a manufacturing process for a wiring board sheet;

FIGS. 8( a) to 8(c) are cross sectional views showing still anotherexample of a manufacturing process for a wiring board sheet;

FIGS. 9( a) to 9(c) are cross sectional views showing still anotherexample of a manufacturing process for a wiring board sheet;

FIGS. 10( a) to 10(d) are cross sectional views showing still anotherexample of a manufacturing process for a wiring board sheet;

FIGS. 11( a) to 11(c) are cross sectional views showing still anotherexample of a manufacturing process for a wiring board sheet;

FIG. 12( a) is a cross sectional view showing a base for transcriptionon which a conductor circuit has been formed and FIG. 12( b) is a crosssectional view showing the base for transcription where electriccomponents have additionally been mounted on the conductor circuit;

FIG. 13( a) is a plan view showing another example of a base fortranscription on which a conductor circuit has been formed and FIG. 13(b) is a cross sectional view of FIG. 13( a);

FIGS. 14( a) and 14(b) are cross sectional views showing a process offorming a resin sheet;

FIGS. 15( a) to 15(d) are cross sectional views showing a process offorming a resin layer having through holes in which a conductivematerial is filled;

FIGS. 16( a) to 16(c) are cross sectional views showing an example of amanufacturing process for a sheet;

FIGS. 17( a) to 17(c) are cross sectional views showing another exampleof a manufacturing process for a sheet;

FIGS. 18( a) and 18(b) are cross sectional views showing still anotherexample of a manufacturing process for a sheet;

FIGS. 19( a) to 19(c) are cross sectional views showing still anotherexample of a manufacturing process for a sheet;

FIGS. 20( a) to 20(e) are cross sectional views showing still anotherexample of a manufacturing process for a sheet;

FIGS. 21( a) to 21(c) are cross sectional views showing the stepsfollowing the step shown in FIG. 20( e);

FIGS. 22( a) to 22(c) are cross sectional views showing an example of amanufacturing process for a multilayer board;

FIGS. 23( a) to 23(c) are cross sectional views showing another exampleof a manufacturing process for a multilayer board;

FIGS. 24( a) and 24(b) are cross sectional views showing still anotherexample of a manufacturing process for a multilayer board;

FIGS. 25( a) and 25(b) are cross sectional views showing still anotherexample of a manufacturing process for a multilayer board;

FIGS. 26( a) and 26(b) are cross sectional views showing still anotherexample of a manufacturing process for a multilayer board;

FIGS. 27( a) to 27(c) are cross sectional views showing still anotherexample of a manufacturing process for a multilayer board;

FIGS. 28( a) to 28(c) are cross sectional views showing still anotherexample of a manufacturing process for a multilayer board;

FIGS. 29( a) to 29(c) are cross sectional views showing still anotherexample of a manufacturing process for a multilayer board;

FIGS. 30( a) and 30(b) are cross sectional views showing still anotherexample of a manufacturing process for a multilayer board;

FIGS. 31( a) to 31(c) are cross sectional views showing still anotherexample of a manufacturing process for a multilayer board;

FIGS. 32( a) to 32(c) are cross sectional views showing still anotherexample of a manufacturing process for a multilayer board; and

FIGS. 33( a) to 33(c) are cross sectional views showing sill anotherexample of a manufacturing process for a multilayer board.

EXPLANATION OF SYMBOLS

-   1 wiring board sheet-   3 through holes-   4 resin layer-   5 conductor circuit-   5 a ground layer-   6 base for transcription-   7 carrier base-   8 conductive paste-   9 metal foil-   10 electric components-   11 multilayer board-   12 protective film-   13 sheet-   17 metal foil with resin-   18 hole plating-   19 through holes-   20 resin paste

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the present invention are described in thefollowing.

A wiring sheet 1 is fabricated by transcribing a conductor circuit 5that has been placed on a base 6 for transcription to a resin layer 4 inthe B-stage, and by burying electric components 10 that have beenmounted on this conductor circuit in the resin layer 4.

FIG. 12( a) shows the base 6 for transcription on a surface of which theconductor circuit 5 has been placed. A method for forming the conductorcircuit 5 on the base 6 for transcription is not particularly limited,and the conductor circuit 5 can be formed by carrying out an etchingprocess after a metal foil such as a copper foil has been adhered to thebase 6 for transcription. However, in the case where the formation ofthe conductor circuit 5 is carried out through pattern plating by meansof electrolyte copper plating or the like, a microscopic conductorcircuit 5 can be easily formed, and in addition, the conductor circuit5, having two smooth surfaces, can be easily formed so that the highfrequency loss of the ultimately completed wiring board can be reducedso as to increase the reliability in the high frequency. It ispreferable for this conductor circuit 5 to be formed so as to have athickness of from 5 μm to 35 μm.

The formation of the conductor circuit by means of a plating treatmentis carried out in a manner where after the formation of a plating resiston the surface of, for example, a base for transcription, a conductorcircuit is placed on the base for transcription by carrying out aplating treatment, and after that, the plating resist is released.

The formation of the plating resist is carried out according to ageneral technique using a photosensitive dry film, a resist ink or thelike. In addition, the formation of the conductor circuit by means of aplating treatment can be carried out through the formation of a platingfilm such as copper, nickel or gold, according to a general technique.

In the case where the conductor circuit 5 is formed by means of aplating treatment as described above, it is preferable to carry out asurface treatment to an extent where the high frequency characteristicsare not damaged in order to ensure the adhesiveness between the resinlayer 4, insulator layer 16 and the conductor circuit 5 at the time ofthe below described transcription of the conductor circuit 5. A surfaceroughening treatment by means of, for example, a blackening treatment oran alumite treatment can be cited as the above described surfacetreatment.

As shown in FIG. 12( b), the electric components 10 are mounted onpredetermined positions of the conductor circuit 5 placed on the base 6for transcription as described above. Passive components such asresistors in chip form, capacitors in chip form or inductors in chipform can be mounted as these electric components 10 and at this time thecomponents in chip form can be mounted so as to be connected to theconductor circuit 5 by means of solder 14. In addition, activecomponents such as semiconductor bare chips represented by silicon barechips can be mounted as the electric components 10 and in such a casesemiconductor bare chips can be mounted so as to be connected to theconductor circuit 5 by means of solder balls or the like, whereunderfill is used and cured. An epoxy resin composition, or the like,can be generally used as the underfill.

Here, the mounting of the electric components 10 is not limited to thatby means of solder 14, but rather the mounting can be carried out usinga conductive paste though the connection by means of solder 14 has ahigh reliability in the mounting.

In addition, at least either resistance elements or capacitor elementscan be formed through printing as the electric components 10 atpredetermined positions on the base 6 for transcription on which theconductor circuit 5 has been formed at the time when the electriccomponents 10 are mounted. In the case of the formation through printingof resistance elements (printed resistors) for example, elements of highcapacities can be formed by applying heat to a resistor material afterthe resistor material in paste form, which is made of a thermosettingresin in which metal powder has been mixed, has been printed. Inaddition, in the case of the formation of capacitor elements throughprinting, elements of high capacities can be formed by applying heat toa dielectric material after the dielectric material in paste form, whichis made of a thermosetting resin in which barium titanate, or the like,has been mixed as a high dielectric filler, has been printed. Inparticular, elements having a higher dielectric constant can be formedby sintering and volatilizing the resin content in the paste so that theelements are converted to ceramic form.

In the case where the electric components 10 are formed through printingas described above, it becomes possible to form very thin elements, andthereby, reduction in the thickness of a wiring board can beimplemented. In addition, the electric components are not mounted bymeans of soldering, and therefore, it becomes possible to process awiring board in an already existing facility for processing printedwiring boards.

In addition, capacitance values or resistance values are adjusted bytrimming the electric components that have been formed through printingusing a laser, and in such a case, there may be a risk of negativeeffects occurring such as damage to the board due to heat, thermalcontraction, reduction in the reliability of the board due to thermaldeterioration when the elements are formed directly on a wiring boardsuch as FR-4 type, or the like, through printing. Contrarily, a laserprocess can be carried out in the condition where the electriccomponents 10 are mounted on the base 6 for transcription when theelectric components 10 are formed on the base 6 for transcriptionthrough printing and the process can be carried out without taking intoconsideration damage of the base, negative effects on the body of thewiring board sheet due to heat, or the like.

The above described conductive circuit 5 is formed so that the adhesionstrength (peel strength) between the base 6 for transcription andconductive circuit 5 becomes preferably in a range of from 0.098 mN/cmto 1.96 mN/cm (10 gf/cm to 200 gf/cm) and more preferably in a range offrom 0.294 mN/cm to 0.882 mN/cm (30 gf/cm to 90 gf/cm) and in such arange a sufficient adhesion between the base 6 for transcription and theconductor circuit 5 can be gained and the release properties of the base6 for transcription from the conductor circuit 5 are enhanced at thetime when the conductor circuit 5 is transcribed to the resin layer 4 orinsulation layer 16. In addition, in the case where the connections aremade using solder 14, the conductor circuit 5 is prevented from beingreleased from the base 6 for transcription so that the mounting can becarried out easily using solder 14 and a high reliability can be gainedin the connection between the electric components 10 and the conductorcircuit 5 when heat resistance of the base 6 for transcription is highand heat is applied at the time of connection by means of solder 14. Inthe case where such adhesion strength is too small, adhesion between theconductor circuit 5 and the base 6 for transcription becomesinsufficient, while in the case where such adhesion strength is toolarge there is a risk of a failure in completely releasing the base 6for transcription from the conductor circuit 5 at the time when theconductor circuit 5 is transcribed to the resin layer 4 from the base 6for transcription.

It is preferable to use a metal base as the above described base 6 fortranscription and in the case where a stainless steel base is used, highreleasing properties of the base from the resin layer 4 and from theconductor circuit 5 can be gained at the time of transcription of theconductor circuit 5 so that the conductor circuit 5 can be easilytranscribed to the resin layer 4 due to stainless steel having a lowadhesiveness vis-à-vis the conductor circuit 5 made of metal such ascopper and the resin layer 4. SUS304 and SUS301 are preferable as thestainless steel base, and in particular SUS301 is excellent from thepoint of view of adhesiveness of plating.

In the case where a stainless steel base is used, it is preferable forthe thickness to be from 50 μm to 200 μm and in particular, handling isgood when the thickness is approximately 100 μm. That is to say, in thecase where a stainless steel base having a thickness of from 50 μm to200 μm, in particular, a thickness of 100 μm is used, the base 6 fortranscription has a high tenacity and an appropriate flexibility so thathandling is good because the base 6 for transcription can be easilyreleased from the resin layer 4 while flexing the base 6 fortranscription without the curvature of the resin layer 4 at the timewhen the base 6 for transcription is released from the resin layer 4 inorder to transcribe the conductor circuit 5 as described below. Inaddition, when a stainless steel base is used as described above thetenacity of the base 6 for transcription is enhanced so that thehandling becomes good even in the case where a great number of electriccomponents 10 are mounted in a manner where, for example, actions suchas carrying the base into and taking the base out from a reflow furnacein the case where a great number of electric components 10 are mountedon the conductor circuit 5 can be easily carried out. In addition, evenin the case where the surface of the base becomes dirty at the time offormation of the conductor circuit 5 or at the time of the mounting ofthe electric components 10, the base can be easily cleaned throughdegreasing, or the like, after the formation of the conductor circuit 5or after the mounting of the electric components 10 so that no stainsare transcribed to the resin layer 4 preventing a reduction in thereliability.

In the case where such a stainless steel base is used, adhesivenessbetween the base 6 for transcription and the conductor circuit 5 issecured to a certain degree at the time of the formation of theconductor circuit 5 on the base 6 for transcription by means of platingtreatment, or the like, so as to prevent the conductor circuit 5 frombeing released from the base 6 for transcription in an unprepared mannerat the time of heat application during solder reflow and so as to makethe conductor circuit 5 remain on the resin layer 4 side without failafter the release of the conductor circuit 5 from the base 6 fortranscription at the time of the transcription of the conductor circuit5 where the base 6 for transcription is released from the resin layer 4.In order to do so, it is preferable to adjust the adhesion strengthbetween the base 6 for transcription and the conductor circuit 5 bycarrying out a roughening treatment by means of chemical polishing, forexample, by carrying out a soft etching treatment using an etchant, suchas a mixed acid of nitric acid and hydrofluoric acid or ferric chloride,on the surface of the base 6 for transcription on which the conductorcircuit 5 is to be formed and as a result of such a treatment, thedegree of surface roughness, Ra, of the base 6 for transcription ispreferably made to be 2 μm or less and the degree of surface roughness,Ra, of the base 6 for transcription is more preferably made to be 0.1 μmto 0.5 μm.

In addition, in the case where the conductor circuit 5 for power supplyor for grounding is formed, the conductor circuit 5 may be formed inplain form on the base 6 for transcription and more preferably theconductor circuit 5 is formed in mesh form. In this case, heat stress isrelieved at the time when stress is received due to heat even when thecoefficients of thermal expansion of the base 6 for transcription madeof a stainless steel base, or the like, and of the conductor circuit 5made of copper, or the like, differ from each other, and thereby, theconductor circuit 5 can be prevented from being released from the base 6for transcription in an unprepared manner. In the same manner, it ispreferable to form independent conductor circuits in advance of whichthe number is equal to the number of small pieces in the case when thesmall pieces are cut out from one wiring board.

On the other hand, the resin composite for forming the resin layer 4contains a resin content and an inorganic filler wherein the resincontent contains a thermosetting resin in which a curing agent, a curingaccelerator, a surface treatment agent, and the like, are mixed ifnecessary. In addition, a solvent can be mixed for adjusting theviscosity.

Though the thermosetting resin is not particularly limited, known epoxyresins, phenol resins, cyanate resins and the like, can be cited and oneor more types from among these can be used. In addition, though a fireretardant may be added in addition to a thermosetting resin in order toprovide fire retardancy, an improvement of fire retardancy can beachieved while maintaining a sufficient heat resistance and mechanicalstrength when a thermosetting resin of which a portion or the entiretyis brominated or is modified by adding phosphorous is particularly used.

In the case where a curing agent or a curing accelerator is mixed, thetypes of these are not particularly limited, but rather an appropriateamount of appropriate curing agent or curing accelerator is mixed inaccordance with the utilized thermosetting resin. In the case where anepoxy resin is mixed as the thermosetting resin, for example, a curingagent of a known epoxy resin such as a phenolic novolac resin ordicyandiamide can be mixed as the curing agent, and a known curingaccelerator such as 2-ethyl-4-methyl imidazole or triphenylphosphine canbe mixed as the curing accelerator.

In addition, an appropriate coupling agent such as a silane-basedcoupling agent or a titanate-based coupling agent or an appropriatedispersing agent such as a phosphate ester-based dispersing agent or anether amine-based dispersing agent can be mixed as the surface treatmentagent.

In addition, it is preferable to utilize a solvent having a low boilingpoint, and in this case, a mixed solvent that is mixed in the resincomposition is utilized, and thereby, the surface form of the resinlayer 4 that is formed of the resin composition becomes good after beingdried. It is especially preferable to utilize methyl ethyl ketone,acetone or the like, as such a solvent. In the case where a solventhaving a high boiling point is used, the possibility of the solvent toremain without being sufficiently volatilized at the time of drying ishigh, and there is a risk of the solvent causing the reduction in theelectrical insulation and in the mechanical strength of insulation layer16 that is formed by curing the resin layer 4.

A high volume of the inorganic filler is filled into the resincomposition, and thereby, the rates of thermal expansion of the resinlayer 4, that is formed of the resin composition, and of insulationlayer 16 that is gained by curing and forming this resin layer 4, arelowered, so that the matching of the coefficients of thermal expansion,vis-à-vis the metal that forms the conductor circuit 5 at the time ofthe formation of the wiring board or electrical components 10, can beincreased. The amount of inorganic filler in the mixture at this time ispreferably 80 wt. % to 95 wt. % relative to the entire amount of thecomposition, excluding the solvent, and thus, the coefficient of thermalexpansion of insulation layer 16 becomes 20 ppm/° C. or lower, having anappropriately low level of thermal expansion, and exhibiting bettermatching of coefficients of thermal expansion vis-à-vis the metal thatforms the conductor circuit 5 and the electric components 10, whereinthe occurrence of defects such as separation of insulation layer 16 fromthe conductor circuit 5, damage to the electric components 10, ordisconnection of wires, can be prevented when stress due to heat isreceived.

Aluminum oxide (Al₂O₃), magnesium oxide (MgO), boron nitride (BN),aluminum nitride (AlN), silica (SiO₂), titanium oxide (TiO₂), aluminumborate (9Al₂O₃.2B₂O₃) or the like can be used as the inorganic filler,where one type of these can be used solely, or two or more types can becombined. A high volume of these inorganic fillers can be easily filledinto the composition in accordance with an appropriate grain design inthe case where a desired function is selected, providing a high level offreedom in thermal conductivity, dielectric constant, distribution ofgrain size and color tone. In particular, in the case where inorganicfiller, of which the maximum grain diameter is 10 μm or less, is used,shapes of holes and state of wear can be maintained in good conditionduring the creation of the through holes 3 by means of laser processing,or drill processing. In addition, a good appearance can be achieved evenin the case where the resin sheet is a thin film having a thickness of50 μm or less.

In addition, it is preferable to add an appropriate amount of couplingagent, such as an epoxy silane based coupling agent or a titanate basedcoupling agent, or an appropriate amount of dispersing agent, such as aphosphate ester based dispersing agent of an ether amine baseddispersing agent in order to increase the dispersion of inorganic fillerin the composition.

In addition, a thermoplastic resin, such as a phenoxy resin, can bemixed in order to adjust the fluidity or in order to prevent cracking inthe resin layer 4 or the insulation layer that is the cured resin.

A thermosetting resin composition can be gained by slurrying all of theabove described components using a kneader, and by adjusting theirviscosity to the optimal level.

A synthesized resin film, such as a PET film, or a metal foil, can beused as a carrier base 7 for forming the resin layer 4. In the casewhere a metal foil is used, it is preferable to make the surface onwhich the resin layer 4 is formed a mirror surface, in order to improvethe release properties of the carrier base 7 at the time when thecarrier base 7 is released from the resin layer 4. A material thatallows for the creation of the through holes 3 by means of laserprocessing is selected as such a metal foil, and it is preferable to usea rolled copper foil, an electrolytic copper foil, an aluminum foil, ametal alloy foil, a metal clad foil, or the like.

A resin sheet 4 a is formed on one surface of this carrier base 7 inorder to form the resin layer 4. In order to form resin sheet 4 a, asshown in FIG. 14( a), the above described resin composition is firstapplied to one surface of the carrier base 7, which is heated and driedso as to be converted to a semi-cured condition (the B-stage), and thus,the resin sheet 4 a is formed on the surface of the carrier base 7.Though the heating and drying conditions at this time depend on themakeup of the resin composition, heating at 130° C. to 170° C. for 2 to10 minutes is preferable. In addition, it is preferable to form resinsheet 4 a so as to have a thickness of 50 μm to 300 μm.

Then, as shown in FIG. 14( b), the carrier base 7 is released from theabove described formed resin sheet 4 a.

In addition, a resin sheet formed by impregnating a resin composition inslurry form into an unwoven cloth, which is then dried, can be used asthe resin sheet 4 a. An appropriate glass unwoven cloth, an organicfiber unwoven cloth, or the like, can be used as the unwoven cloth.

The above described resin sheet 4 a and the base 6 for transcription ona surface of which the conductor circuit 5, to be later transcribed, hasbeen formed, and the electric components 10 have been mounted on thisconductor circuit 5 are used so that the conductor circuit 5 can betranscribed from the base 6 for transcription to the resin layer 4, thathas been formed from the resin sheet 4 a, and thereby, the wiring boardsheet 1 is gained, wherein conductor circuits 5 are formed on the twosurfaces, and the electric components 10 mounted on these conductorcircuits 5 are buried in resin layers 4.

FIGS. 1( a) to 1(c) show an example of a manufacturing process for thewiring board sheet 1. First, as shown in FIG. 1( a), the bases 6 fortranscription, where conductor circuits 5 have been formed and theelectric components 10 have been mounted on these conductor circuits 5,are placed so that the surfaces on which the conductor circuits 5 havebeen formed are opposite to each other while resin sheets 4 a are placedbetween these bases, and then, these bases and the resin sheets arelayered. There may be one or more resin sheets 4 a, and this number isdependent on the dimensions of protrusions of the electric components 10from the conductor circuits 5. In this condition, heating and pressingmolding is carried out so as to integrate the layers.

First, in this molding process, the resin sheets 4 a are melted andsoftened. At this time, in the case where two or more resin sheets 4 aare layered, these resin sheets 4 a are integrated, and moreover, thesemelted and softened resin sheets 4 a are sufficiently fluidized so thatthe conductor circuits 5, that have been formed on the bases 6 fortranscription, as well as the electric components 10, that have beenmounted on the conductor circuits 5, are buried in the resin layer 4which is formed from the resin sheets 4 a. At this time, in the casewhere no underfill is placed beneath the electric components 10, theprocess is carried out in a condition where the melted and softened theresin layer 4 are fluidized sufficiently so that an adequate amount ofresin is filled between the electric components 10 and the bases 6 fortranscription. In addition, the pressure at the time of molding needs tobe set in accordance with the fluidity of the resin layer 4 when beingmelted and softened, and in the case where this level of fluidity whenbeing melted and softened is high, for example, molding can be carriedout easily using a vacuum laminator, while in the case where the levelof fluidity when being melted and softened is low, molding can becarried out under pressure of up to approximately 2.94 MPa (30 kgf/cm²)In addition, it is preferable to gradually increase the pressure fromthe point in time when resin sheets 4 a have been melted and softened inorder for the electric components 10 to be buried in the resin layer 4.Furthermore, it is preferable to carry out this heating and pressingmolding under reduced pressure, or in a vacuum, and under suchconditions, the possibility of voids being created internally isreduced, enhancing reliability.

Next, as shown in FIG. 1( c), the bases 6 for transcription are releasedfrom the resin layer 4 while the conductor circuits 5 are made to remainon the resin layer 4, and thereby, the wiring board sheet 1 (the wiringboard sheet 1 a) is gained. This wiring board sheet 1 a is formed sothat the conductor circuits 5 are buried in the surface layers on bothsides of the resin layer 4, so as to be exposed from the surface of theresin layer 4, where the external surfaces of the resin layer 4 and theexposed surfaces of the conductor circuits 5 are in the same planeshaving flat surfaces without unevenness. In addition, the electriccomponents 10, which are connected to the respective conductor circuits5 on both sides, are buried in the resin layer 4.

The bases 6 for transcription can be released from the resin layer 4 bystripping the bases 6 for transcription, starting from edges of theresin layer 4. These bases 6 for transcription, after being releasedfrom the resin layer 4, can be utilized again in the manufacturing ofthe wiring board sheet 1, wherein conductor circuits 5 are formed onthese bases after being cleaned by means of acid cleaning.

In the case where the above described heating and pressing molding iscarried out, in the condition where the curing response of the resinlayer 4 progresses, a wiring board (two-sided board) can be gainedwherein conductor circuits 5 are placed on both sides and electricalconnections 10, electrically connected to each of the conductor circuits5, are buried in the insulation layer that is formed of the cured resinlayer 4. Though the heating temperature at this time depends on themakeup of the resin composition that forms the resin layer 4, it ispreferable to carry out the heating at a temperature ranging from 160°C. to 180° C.

In addition, in the case where the above described heating and pressingmolding is carried out under conditions where the resin layer 4 ismaintained in the B-stage, the gained wiring board sheet 1 a can beutilized in the manufacturing of a multilayer board 11 as describedbelow. Though the molding conditions at this time depend on the makeupof the resin composition that forms the resin layer 4, it is preferableto carry out the heating at a temperature ranging from 100° C. to 140°C. for 2 to 10 minutes. Furthermore, in the case where the wiring boardsheet 1 a is used as the core material for the formation of a multilayerboard, the wiring board sheet 1 a can be utilized for the manufacturingof a multilayer board 11 even when the resin layer 4 moves into theC-stage.

FIGS. 2( a) to 2(c) show another example of a manufacturing process forthe wiring board sheet 1, wherein resin sheets 4 a; the base 6 fortranscription on a surface of which the conductor circuit 5, to be latertranscribed, has been formed, and the electric components 10 have beenmounted; and the base 6 for transcription on a surface of which theconductor circuit 5, to be later transcribed, has been formed, and noelectric components 10 have been mounted, are used so that conductorcircuits 5 can be transcribed from the bases 6 for transcription to theresin layer 4 that is formed of resin sheets 4 a, and thereby, thewiring board sheet 1 (the wiring board sheet 1 g) is formed whereinconductor circuits 5 are formed on both sides of the wiring board sheet,and electrical connections 10, mounted on the conductor circuit 5 on oneside, are buried in the resin layer 4.

First, as shown in FIG. 2( a), the base 6 for transcription where theconductor circuit 5 has been formed and the electric components 10 havebeen mounted, and the base 6 for transcription where the conductorcircuit 5 has been formed and no electric components 10 have beenmounted, are placed so that the surfaces on which conductor circuits 5have been formed are opposite to each other and resin sheets 4 a areplaced between the bases, and subsequently, the bases and the resinsheets are layered. One or more resin sheets 4 a are placed, and thisnumber is dependent on the dimensions of the electric components 10.Heating and pressing molding is carried out in this condition, andthereby, the layers are integrated. This heating and pressing moldingcan be carried out in the same conditions as in the above describedcase.

In this molding process, resin sheets 4 a are melted and softened. Atthis time, in the case where two or more resin sheets 4 a are layered,these resin sheets 4 a are integrated, and these melted and softenedresin sheets are fluidized so that conductor circuits 5 that have beenformed on the bases 6 for transcription and the electric components 10that have been mounted on the conductor circuit 5 are buried in theresin layer 4 which are formed of resin sheets 4 a.

Next, as shown in FIG. 2( c), the bases 6 for transcription are releasedfrom the resin layer 4 while conductor circuits 5 are made to remain onthe resin layer 4, and thereby, the wiring board sheet 1 (the wiringboard sheet 1 g) is gained. This wiring board sheet 1 g is formed in amanner where conductor circuits 5 are buried in the surface layers onboth sides of the resin layer 4 so that conductor circuits 5 are exposedfrom the surfaces of the resin layer 4. In addition, the externalsurfaces of the resin layer 4 and the exposed surfaces of conductorcircuits 5 are in the same planes where the surfaces are flat withoutunevenness. Furthermore, the electric components 10 which are connectedto the conductor circuit 5 on one side are buried in the resin layer 4.The bases 6 for transcription can be released from the resin layer 4 bystripping the bases 6 for transcription starting from edges of the resinlayer 4.

When the above described heating and pressing molding is carried outunder a condition where the curing response of the resin layer 4progresses, a wiring board (two-sided board) can be gained wherein theconductor circuit 5 is placed on one side and the electric components 10electrically connected to the conductor circuit 5 are buried in theinsulation layer that is formed of the cured resin layer 4. The heatingtemperature at this time can be made the same as in the above describedcases.

In addition, in the case where the above described heating and pressingmolding is carried out in the condition where the resin layer 4 ismaintained in the B-stage, the gained wiring board sheet 1 g can beutilized in the manufacturing of multilayer board 11 as described below.The molding conditions at this time can be made the same as in the abovedescribed cases. Furthermore, in the case where the wiring board sheet 1g is used as the core material at the time of the formation of amultilayer board, the wiring board sheet can be utilized for themanufacturing of multilayer board 11 even when the resin layer 4 movesto the C-stage.

In addition, as shown in FIGS. 1( c) and 2(c), the through holes 3 whichare filled with conductive material 2 can, additionally, be createdafter the bases 6 for transcription have been released from the resinlayer 4, and thereby, the wiring board sheet 1 (the wiring board sheet 1b) can be gained. One example of such a process is shown in FIGS. 3( a)to 3(d)

First, as shown in FIG. 3( a), a protective film 12 is layered andplaced on one surface of the resin layer 4 of the wiring board sheetshown in FIG. 1( c) to which the conductor circuit 5 has beentranscribed. A synthesized resin film such as a PET film, or a metalfoil, can be used as the protective film 12. In the case where a metalfoil is used, it is preferable to make the surface on which the resinlayer 4 is formed a mirror surface in order to improve the releaseproperties of the protective film 12 at the time when the protectivefilm 12 is released from the resin layer 4. A material that allows forthe creation of the through holes 3 at the time of laser processing isselected as such a metal foil, and it is preferable to use a rolledcopper foil, an electrolytic copper foil, an aluminum foil, a metalallow foil, a metal clad foil, or the like, and a foil to which adhesivehas been applied to a surface is preferable.

Next, as shown in FIG. 3( b), the through holes 3 are created inpredetermined positions of the resin layer 4 for creating via holes bymeans of laser processing. These through holes 3 are created so as topenetrate predetermined portions of the resin layer 4, the protectivefilm 12 and conductor circuits 5 on both sides of the resin layer 4. Atthis time, the protective film 12 side is irradiated with a laser beampreventing the resin layer 4 and conductor circuits 5 from beingdirectly irradiated with the laser beam, so that the protective film 12can be prevented from being released from the resin layer 4 due to thelaser beam.

After the creation of the through holes 3, as shown in FIG. 3( c), thethrough holes 3 are filled in with conductive material 2 from theexternal surface side of the protective film 12. The conductive paste 8can be used as this conductive material 2, which is, for example, athermosetting resin composition into which conductive powder such assilver or copper powder has been mixed. In order to fill the throughholes 3 with the conductive paste 8, the conductive paste 8 is appliedto the external surface of carrier base 7 so that the conductive paste 8fills the through holes 3 from the openings of the through holes 3. Atthis time, the external surface of the resin layer 4 is protected bycarrier base 7 by not allowing the conductive paste 8 to adhere to theexternal surface of the resin layer 4, and subsequently, the protectivefilm 12 to the external surface of which the conductive paste 8 hasadhered is released from the resin layer 4 side as shown in FIG. 3( d)after the through holes have been filled with the conductive paste 8. Asa result, a condition is achieved wherein the through holes 3 are filledin with the conductive paste 8 and the conductive paste 8 is not adheredto the external surfaces of the resin layer 4 and conductor circuits 5.In addition, the conductive paste 8 that has filled in the through holes3 of carrier base 7 remains in a manner where the conductive paste 8protrudes outward from the through holes 3 of the resin layer 4 on theside to which the protective film 12 has been adhered.

Here, the through holes 3 filled with conductive material 2 are createdafter the conductor circuit 5, on which the electric components 10 havebeen mounted, has been transferred to the resin layer 4, because theresin layer 4 are fluidized as the electric components 10 are buriedinto the resin layer 4 at the time when the conductor circuit 5, onwhich the electric components 10 have been mounted, are transferred tothe resin layer 4, and at this time, there is a risk of the shapes ofthe through holes 3 being deformed in the case where the through holes 3have been created. In order to prevent deformation of the through holes3, created in order to form such via holes, the through holes 3 arecreated after the electric components 10 have been buried in the resinlayer 4.

The wiring board sheet 1 b is formed as described above, whereinconductor circuits 5 are buried in the surface layers on both sides ofthe resin layer 4 so that conductor circuits 5 are exposed from thesurfaces of the resin layer 4, and in addition, the electric components10, which are connected to the respective conductor circuits 5 on bothsides, are buried in the resin layer 4. Furthermore, the through holes 3are created so as to penetrate the resin layer 4 and conductor circuits5, and so as to be filled with the conductive paste 8. The surfaces ofthis wiring board sheet 1 b are formed into a flat state withoutunevenness except for the conductive paste 8 protruding from thesurfaces where the external surfaces of the resin layer 4 and theexposed surfaces conductor circuits 5 are in the same planes.

A single wiring board sheet 1 b, gained in the above described manner,can be used in the manufacturing of a wiring board. In this case, theabove described heating and pressing molding, at the time oftranscription of conductor circuits 5, on which the electric components10 have been mounted to the resin layer 4, may be carried out inconditions where the curing response of the resin layer 4 progresses, orwhere such curing response does not progress, and additional heating andpressing molding is carried out on the gained wiring board sheet 1 b inorder to gain a wiring board (two-sided board) wherein the resin layer 4is cured in the case that this has been kept in the B-stage, and theconductive paste 8 is cured so that conductor circuits 5 are gained onboth sides of the wiring board while the electric components 10, thatare electrically connected to the respective conductor circuits 5, aremounted in the insulation layer that is formed of the cured resin layer4, and in addition, conductor circuits 5, on both sides of the wiringboard, are connected to each other through via holes that are formedfrom the cured conductive paste 8 within the through holes 3.

During this molding process, the protruding portions of the conductivepaste 8 are pressed into the through holes 3 by applying pressure sothat the conductive paste in the through holes is compressed, andthereby, the reliability of the connections of the via holes isincreased.

In addition, in the case where the above described heating and pressingmolding at the time when conductor circuits 5 on which the electriccomponents 10 have been mounted are transferred to the resin layer 4, iscarried out in the condition where the resin layer 4 and the conductivepaste 8 are maintained in the B-stage, the gained wiring board sheet 1 bcan be utilized for the manufacturing of multilayer board 11 asdescribed below. In this case, the above described protrusions of theconductive paste 8 contribute to the increase in conductivity of viaholes 15 in multilayer board 11 as described below. In addition, in thecase where the wiring board sheet 1 b is used as the core material atthe time of the formation of a multilayer board, the wiring board sheetcan be utilized for the manufacturing of multilayer board 11 even whenthe resin layer 4 is in the C-stage.

FIGS. 4( a) to 4(c) shows another example of the manufacturing processfor the wiring board sheet 1, wherein resin sheets 4 a, and the base 6for transcription, where the conductor circuit 5, to be latertranscribed, has been formed on a surface, are used so that theconductor circuit 5 is transcribed from the base 6 for transcription tothe resin layer 4 formed of resin sheets 4 a, and thereby, the wiringboard sheet 1 (the wiring board sheet 1 c) is formed wherein theconductor circuit 5 is formed on one side of the wiring board sheet andthe electric components 10, mounted on this conductor circuit 5, areburied in the resin layer 4.

First, as shown in FIG. 4( a), resin sheets 4 a are placed and layeredon the base 6 for transcription, on which the conductor circuit 5 hasbeen formed, and the electric components 10 have been mounted on thisconductor circuit 5 on the side on which this conductor circuit 5 hasbeen formed on the surface. One or more resin sheets 4 a are used inaccordance with the dimensions of the electric components 10. Heatingand pressing molding is carried out in this condition, and thereby, theresin sheets and the conductor circuit are integrated. This heating andpressing molding can be carried out in the same conditions as in theabove described cases.

In this molding process, resin sheets 4 a are melted and softened. Atthis time, in the case where two or more resin sheets 4 a are layered,these resin sheets 4 a are integrated and these melted and softenedresin sheets 4 a are fluidized, and thereby, the conductor circuit 5,formed on the base 6 for transcription, and the electric components 10,mounted on the conductor circuit 5, are buried in the resin layer 4formed of resin sheets 4 a.

Next, as shown in FIG. 4( c), the base 6 for transcription is releasedfrom the resin layer 4 while the conductor circuit 5 is made to remainin the resin layer 4, and thereby, a wiring board sheet 1 c is gained.This wiring board sheet 1 c is formed in a manner where the conductorcircuit 5 is buried in a surface layer on one side of the resin layer 4so that the conductor circuit 5 is exposed from the surface of the resinlayer 4. In addition, the external surface of the resin layer 4, and theexposed surface of the conductor circuit 5, are in the same plane, andare formed into a flat state without unevenness. In addition, theelectric components 10, connected to the conductor circuit 5 on oneside, are buried in the resin layer 4. The base 6 for transcription canbe released from the resin layer 4 by stripping the base 6 fortranscription starting from an edge of the resin layer 4.

In the case where the above described heating and pressing molding iscarried out in the condition where the curing response of the resinlayer 4 progresses, a wiring board (one-sided board) can be gained,wherein the conductor circuit 5 is gained on one side of the wiringboard, and the electric components 10, electrically connected to theconductor circuit 5, are buried in the insulation layer formed of thecured resin layer 4. The heating temperature at this time can be set atthe same temperature as in the above described cases.

In addition, in the case where the above described heating and pressingmolding is carried out in the condition where the resin layer 4 ismaintained in the B-stage, the gained wiring board sheet 1 can beutilized for the manufacturing of multilayer board 11 as describedbelow. The molding conditions at this time can be set at the same levelsas in the above described cases. Furthermore, in the case where thewiring board sheet 1 is used as the core material at the time of forminga multilayer board, the wiring board sheet can be utilized for themanufacturing of multilayer board 11, even when the resin layer 4 is inthe C-stage.

In addition, as shown in FIG. 4( c), the wiring board sheet 1 (thewiring board sheet 1 d) can be gained where the through holes 3 arecreated in the resin layer 4, to which the conductor circuit 5, on whichthe electric components 10 have been mounted, has been transferred, andfurthermore, the through holes 3 are filled with conductive material 2.An example of this process is shown in FIG. 5.

First, as shown in FIG. 5( a), the protective film 12 is layered andplaced on the side of the resin layer 4, to which the conductor circuit5 has been transcribed, where the conductor circuit 5 has not beenformed on the surface. The same protective film as described above canbe used as the protective film 12.

Next, as shown in FIG. 5( b), the through holes 3 are created inpredetermined positions where via holes are to be formed on the resinlayer 4 by means of laser processing. These through holes 3 are createdso as to penetrate predetermined positions of the resin layer 4, theprotective film 12 and the conductor circuit 5 on one side of the resinlayer 4. At this time, the protective film 12 side is irradiated with alaser beam, and thereby, the protective film 12 can be prevented frombeing released from the resin layer 4 due to the laser beam.

After the creation of the through holes 3, as shown in FIG. 5( c), thethrough holes 3 are filled with conductive material 2 from the externalsurface side of the protective film 12. The conductive paste 8 can beused as this conductive material 2, which is, for example, athermosetting resin composition into which conductive powder, such assilver or copper powder, has been mixed. The through holes 3 are filledwith the conductive paste 8 from the openings of the through holes 3, byapplying the conductive paste 8 to the external surface of carrier base7, in order to fill the through holes with the conductive paste 8. Atthis time, the external surface of the resin layer 4 is protected bycarrier base 7 by not allowing the conductive paste 8 to adhere to theexternal surface of the resin layer 4, and subsequently, as shown inFIG. 5(d), the protective film 12, where the conductive paste 8 hasadhered to the external surface, is released from the resin layer 4 sideafter the through holes have been filled with the conductive paste 8,and thereby, a condition is achieved where the through holes 3 arefilled with the conductive paste 8, and no conductive paste 8 is adheredto the external surfaces of the resin layer 4 and the conductor circuit5. In addition, the conductive paste 8 that has filled in the throughholes 3 of carrier base 7 remains, and therefore, the conductive paste 8protrudes outward from the through holes 3 of the resin layer 4 on thesurface, on the side where the protective film 12 has been adhered (thesurface on the side where the conductor circuit 5 has not been formed).

In the wiring board sheet 1 d that is gained as described above, theconductor circuit 5 is buried in a surface layer on one side of theresin layer 4 so that the conductor circuit 5 is exposed from thesurface of the resin layer 4 and the electric components 10 areconnected to the conductor circuit 5 on one side of the resin layer 4and are buried in the resin layer 4, wherein the through holes 3 arecreated so as to penetrate the resin layer 4 and the conductor circuit 5on one side of the resin layer 4, and are filled in with the conductivepaste 8. The surface of this wiring board sheet 1 b is formed into aflat state without unevenness, except for the protruding conductivepaste 8, where the external surface of the resin layer 4 and the exposedsurface of the conductor circuit 5 are in the same plane.

Here, after the conductor circuit 5, on which the electric components 10have been mounted, has been transcribed to the resin layer 4, thethrough holes 3 filled with conductive material 2 are created, becausethe resin layer 4 is fluidized as the electric components 10 are buriedinto the resin layer 4 at the time when the conductor circuit 5, onwhich the electric components 10 have been mounted, is transcribed tothe resin layer 4, and at this time, in the case where the through holes3 have been created, there is a risk of the shapes of the through holes3 being deformed to a large extent. In order to prevent such deformationof the through holes 3, created to form via holes 15, the through holes3 are created after the electric components 10 have been buried in theresin layer 4.

Here, in the case where the above described heating and pressing moldingis carried out in the condition where the resin layer 4 is maintained inthe B-stage, this wiring board sheet 1 d can be utilized for themanufacturing of multilayer board 11 as described below. The moldingconditions at this time can be set at the same levels as in the abovedescribed cases. In addition, in the case where the wiring board sheet 1d is used as the core material for forming a multilayer board, thewiring board sheet can be utilized for the manufacturing of multilayerboard 11, even when the resin layer 4 is in the C-stage.

In addition, as shown in FIG. 5( d), the metal foil 9 can be layered onthe surface of the resin layer 4, to which the conductor circuit 5, onwhich the electric components 10 have been mounted, has beentranscribed, where the conductor circuit has not been formed so that thewiring board sheet 1 (the wiring board sheet 1 e) can be gained. FIGS.6( a) and 6(b) show an example of such a process.

First, as shown in FIG. 6( a), the metal foil 9 is layered and placed onthe surface of the resin layer 4 on the side where the conductor circuit5 has not been formed. An appropriate metal foil, for example, a copperfoil, can be used as the metal foil 9. It is preferable for thethickness of this foil to be in the range of 10 μm to 150 μm. Inaddition, it is preferable for the surface of this metal foil 9 on whichthe resin layer 4 is formed to be a rough surface in order to ensure theadhesiveness vis-à-vis the resin layer 4. In the case where anelectrolytic copper foil, for example, is used as the metal foil 9, theresin layer 4 can be formed on the rough surface of the electrolyticcopper foil, which has been originally formed having a rough surface. Inaddition, a surface roughening treatment by means of, for example, ablackening treatment or an alumite treatment can be cited as thissurface treatment. Heating and pressing molding is carried out in thiscondition, and thereby, the metal foil and the resin layer are layeredand integrated as shown in FIG. 6( b).

In this molding process, the metal foil 9 is electrically connected tothe conductive paste 8 that has filled the through holes 3. In addition,the portions of the conductive paste 8 protruding from the through holes3 are pressed into the through holes 3 by applying pressure so as tocompress the conductive paste within the through holes 3, and thereby,the conductivity of the conductive paste 8 within the through holes 3increases.

In the wiring board sheet 1 e that is gained as described above, theconductor circuit 5 is buried in a surface layer on one side of theresin layer 4 so that the conductor circuit 5 is exposed from thesurface of the resin layer 4, and the metal foil 9 is layered on theother side, wherein the electric components 10 connected to theconductor circuit 5 on one side of the resin layer 4 is buried in theresin layer 4. In addition, the external surface of the resin layer 4and the exposed surface of the conductor circuit 5 are in the same planeso that the surface of the wiring board sheet 1 e is formed into a flatstate without unevenness. Furthermore, the through holes 3 are createdso as to penetrate the resin layer 4 and the conductor circuit 5 and arefilled in with the conductive paste 8 so as to be connected to the metalfoil 9.

In the case where the heating and pressing molding at the time offorming the above described layer of the metal foil 9 is carried out inthe condition where the curing response of the resin layer 4 and theconductive paste 8 progresses, a wiring board can be gained, wherein themetal foil 9 is placed on one surface, and the conductor circuit 5 isplaced on the other surface while the electric components 10, which areelectrically connected to the conductor circuit 5, are buried in theinsulation layer formed of the cured resin layer 4, and furthermore, theconductor circuit 5 and the metal foil 9 are connected through via holesmade of the through holes 3 and filled with a conductive layer formed ofthe cured conductive paste 8. These molding conditions can be set at thesame levels as in the above described cases. In addition, circuits canbe formed from the metal foil 9 of this wiring board by carrying out anetching treatment.

In addition, in the case where the above described heating and pressingmolding, at the time of forming the layered metal foil 9, is carried outin the condition where the resin layer 4 and the conductive paste 8 aremaintained in the B-stage, the gained wiring board sheet 1 can beutilized for the manufacturing of multilayer board 11 as describedbelow. These molding conditions can be set at the same levels as in theabove described cases. Furthermore, in the case where the wiring boardsheet 1 is used as the core material, at the time of forming amultilayer board, the wiring board sheet can be utilized for themanufacturing of multilayer board 11 even when the resin layer 4 is inthe C-stage.

In addition, the wiring board sheet 1 (the wiring board sheet 1 f) canbe gained by forming, through transcription, an additional conductorcircuit 5 on the surface, on which the conductor circuit 5 has not beenformed, of the resin layer 4 shown in FIG. 5( d) to which the conductorcircuit 5, on which the electric components 10 have been mounted, hasbeen transcribed. FIGS. 7( a) and 7(b) show an example of such aprocess.

First, as shown in FIG. 7( a), a base 6 for transcription on which aconductor circuit 5 has been formed is layered and placed on the surfaceof a resin layer 4, on the side where no conductor circuit 5 has beenformed, in the condition where the through holes 3 and the conductorcircuit 5 are positioned on each other, so that the surface on which theconductor circuit has been formed is opposed to resin layer 4. A basefor transcription that has been formed as described above is used as thebase 6 for transcription on which the conductor circuit 5 has beenformed.

Heating and pressing molding is carried out in this condition, andthereby, the base for transcription and the resin layer are layered andintegrated, wherein the conductor circuit 5 and the through holes 3 arepositioned on each other so that predetermined portions of the conductorcircuit 5 are placed at the positions of the openings of the throughholes 3.

In this molding process, the conductor circuit 5, placed on the base 6for transcription, is electrically connected to the conductive paste 8that fills the through holes 3. In addition, the portions of theconductive paste 8 protruding from the through holes 3 are pressed intothe through holes 3 by applying pressure so that the conductive paste iscompressed within the through holes 3, and thereby, the conductivity ofthe conductive paste 8 within the through holes 3 is enhanced.

Next, as shown in FIG. 7( b), the base 6 for transcription is releasedfrom resin layer 4 while the conductor circuit 5 is made to remain inthe resin layer 4, and thereby, a wiring board sheet 1 f is gained.

In the wiring board sheet 1 f that is gained as described above, theconductor circuits 5 are buried in the surface layers on both sides ofthe resin layer 4 so that the conductor circuits 5 are exposed from thesurfaces of the resin layer 4, and the electric components 10, connectedto the conductor circuit 5 on one side of the resin layer 4, is buriedin the resin layer 4. Furthermore, through holes 3 are created so as topenetrate the resin layer 4 and the conductor circuit 5 on one side ofthe resin layer 4, and so as to be filled in with the conductive paste 8that is connected to the conductor circuit 5 on the other side of theresin layer 4. The surfaces of this wiring board sheet 1 f are formedinto a flat state without unevenness in a manner where the externalsurfaces of the resin layer 4 and the exposed surfaces of the conductorcircuits 5 are in the same planes.

In the case wherein the above described heating and pressing molding atthe time of forming the conductor circuits 5 through transcription iscarried out in the condition where the curing response of resin layer 4and the conductive paste 8 progresses, a wiring board can be gainedwherein conductor circuits 5 are placed on both sides and the electriccomponents 10, that are electrically connected to the conductor circuit5 on one side of the resin layer 4, are buried in the insulation layerformed of the cured resin layer 4, and wherein the conductor circuits 5are connected to each other through the via holes made by having throughholes 3 being filled with conductive layers formed of the curedconductive paste 8. These molding conditions can be set at the samelevels as in the above described cases.

In the case where the heating and pressing molding at the time offorming the above described layer of the metal foil 9 is carried out inthe condition where the resin layer 4 and the conductive paste 8 aremaintained in the B-state, the gained wiring board sheet 1 can beutilized for the manufacturing of multilayer board 11 as describedbelow. These molding conditions can be set at the same levels as in theabove described cases. In addition, in the case where the wiring boardsheet 1 is used as the core material at the time of forming a multilayerboard, the wiring board sheet can be utilized for the manufacturing ofmultilayer board 11 even when the resin layer 4 is in the C-stage.

FIGS. 8( a) to 8(c) show another example of a manufacturing process fora wiring board sheet 1, wherein resin sheets 4 a; a base 6 fortranscription where a conductor circuit 5, to be later transcribed, hasbeen formed on a surface and the electric components 10 have beenmounted; and a metal foil 9, such as a copper foil, are used in a mannerwhere the conductor circuit 5 is transcribed from the base 6 fortranscription to a resin layer 4 that is formed of the resin sheets 4 a,and thereby, a wiring board sheet 1 (wiring board sheet 1 h) is formed,wherein the conductor circuit 5 is formed on one surface of the resinlayer, and the electric components 10, that have been mounted on thisconductor circuit 5 on the surface, are buried in the resin layer 4while the metal foil 9 is layered on and integrated with the othersurface of the resin layer.

An appropriate metal foil, for example, a copper foil, can be used asthe metal foil 9. It is preferable for the thickness of this metal foilto be in the range of 10 μm to 150 μm. In addition, it is preferable forthe surface of this metal foil 9, on which the resin layer 4 is formed,to be a rough surface in order to ensure the adhesiveness vis-à-vis theresin layer 4. In the case where an electrolytic copper foil, forexample, is used as the metal foil 9, the resin layer 4 can be formed onthe rough surface of the electrolytic copper foil that has beenoriginally formed having a rough surface. In addition, a surfacetreatment can be carried out on the metal foil 9 and a surfaceroughening treatment by means of, for example, a blackening treatment oran alumite treatment can be cited as this surface treatment.

First, as shown in FIG. 8( a), a base 6 for transcription, where aconductor circuit 5 is formed and the electric components 10 have beenmounted, and a metal foil 9, are placed so that the surface of the base6 for transcription on which the conductor circuit 5 has been formed isopposed to (the rough surface of) the metal foil 9 and resin sheets 4 aare placed between the base for transcription and the metal foil, andthen, the base for transcription, the resin sheets and the metal foilare layered. One or more resin sheets 4 a are used in accordance withthe dimensions of the electric components 10. Heating and pressingmolding is carried out in this condition, and thereby, the base fortranscription, the resin sheets and the metal foil are integrated. Thisheating and pressing molding can be carried out in the same conditionsas in the above described cases.

In this molding process, resin sheets 4 a are melted and softened. Atthis time, in the case where two or more resin sheets 4 a are layered,these resin sheets 4 a are integrated and these melted and softenedresin sheets 4 a are fluidized, and thereby, the conductor circuit 5formed on the base 6 for transcription and the electric components 10,formed on the conductor circuit 5, are buried in the resin layer 4formed of the resin sheets 4 a.

Next, as shown in FIG. 8( c), the base 6 for transcription is releasedfrom the resin layer 4 while the conductor circuit is made to remain inthe resin layer 4, and thereby, a wiring board sheet 1 h is gained. Thiswiring board sheet 1 h is formed in a manner where the conductor circuit5 is buried in a surface layer on one side of the resin layer 4 so thatthe conductor circuit 5 is exposed from the surface of the resin layer 4while a metal foil 9 is formed on and integrated with the entire surfaceon the other side of the resin layer. In addition, the external surfaceof the resin layer 4 and the exposed surface of the conductor circuit 5are in the same plane, and the surfaces are formed into a flat statewithout unevenness. Furthermore, the electric components 10, that havebeen connected to the conductor circuit 5 on one side of the resin layer4, is buried in the resin layer. The base 6 for transcription can bereleased from the resin layer 4 by stripping the base 6 fortranscription from the resin layer 4 starting from an edge of the resinlayer 4.

In the case where the above described heating and pressing molding iscarried out in the condition where the curing response of the resinlayer 4 progresses, the conductor circuit 5 is placed on the surface ofone side of the resin layer and the metal foil 9 is formed on the entiresurface of the other side so that a wiring board can be gained where theelectric components 10, which are electrically connected to theconductor circuit 5, are buried in the insulation layer formed of thecured resin layer 4. The heating temperature at this time can be set atthe same temperature as in the above described cases.

In addition, in the case where the above described heating and pressingmolding is carried out in the condition where the resin layer 4 ismaintained in the B-stage, the gained wiring board sheet 1 h can beutilized for the manufacturing of the multilayer board 11 as describedbelow. The molding conditions at this time can be set at the same levelsas in the above described cases. Furthermore, in the case where thewiring board sheet 1 h is used as the core material at the time offorming a multilayer board, the wiring board sheet can be utilized forthe manufacturing of the multilayer board 11 even when the resin layer 4is in the C-stage.

FIGS. 9( a) to 9(c) shows another example of a manufacturing process fora wiring board sheet 1, wherein resin sheets 4 a; a base 6 fortranscription where a conductor circuit 5, to be later transcribed, isformed on a surface and electric components 10 are mounted; and a metalfoil 17 with resin are used so that the conductor circuit 5 istranscribed from the base 6 for transcription to the resin layer 4formed of the resin sheets 4 a, and thereby, a wiring board sheet 1(wiring board sheet 1 i) is formed where the conductor circuit 5 isformed on one surface and the electric components 10 mounted on thisconductor circuit 5 on the surface are buried in the resin layer 4 andthe metal foil 9 is layered on and integrated with the other surface.

An appropriate metal foil, for example, a copper foil, can be used forthe metal foil 9 that forms the metal foil 17 with resin. It ispreferable for the thickness of this foil to be in the range of 10 μm to150 μm. In addition, it is preferable for the surface of this metal foil9 on which the resin layer 4 is formed to be a rough surface in order toensure the adhesiveness vis-à-vis the resin layer 4. In the case wherean electrolytic copper foil, for example, is used as the metal foil 9,the resin layer 4 can be formed on the rough surface of the electrolyticcopper foil, which has originally been formed having a rough surface. Inaddition, a surface treatment can be carried out on the metal foil 9 anda surface roughening treatment by means of, for example, a blackeningtreatment or an alumite treatment can be cited as this surfacetreatment.

In addition, the resin layer 4 b that forms the metal foil 17 with resincan be formed using a resin composition that is similar to the resincomposition for forming the above described resin layer 4 and, forexample, such a resin composition is applied to one surface (roughsurface) of the metal foil 9 and is then dried so as to be converted tothe B-stage so that the resin layer 4 b is formed and the metal foil 17with resin can be gained.

First, as shown in FIG. 9( a), the base 6 for transcription where theconductor circuit 5 has been formed and the electric components 10 havebeen mounted; and the metal foil 17 with resin are placed so that thesurface of the base 6 for transcription on which the conductor circuit 5has been formed and the resin 4 b of the metal foil 17 with resin areopposite to each other and one or more resin sheets 4 a are placedbetween the base for transcription and the metal foil so that the basefor transcription, the resin sheets and the metal foil are layered. Oneor more resin sheets 4 a are used in accordance with the dimensions ofthe electric components 10. Heating and pressing molding is carried outin this condition so that the layers are integrated. This heating andpressing molding can be carried out in the same conditions as in theabove described cases.

In this molding process, the resin sheets 4 a and the resin layer 4 b ofthe metal foil 17 with resin are melted and softened so as to beintegrated to form the resin layer 4. At this time, in the case wheretwo or more resin sheets 4 a are layered, these resin sheets 4 a areintegrated and the conductor circuit 5 formed on the base 6 fortranscription and the electric components 10 mounted on the conductorcircuit 5 are buried in the resin layer 4 that is formed of the resinsheets 4 a due to the fluidity of these melted and softened resin sheets4 a.

Next, as shown in FIG. 9( c), the base 6 for transcription is releasedfrom the resin layer 4 while the conductor circuit 5 is made to remainin the resin layer 4, and thereby, a wiring board sheet 1 i is gained.This wiring board sheet 1 i is formed in a manner where the conductorcircuit 5 is buried in a surface layer on one side of the resin layer 4so that the conductor circuit 5 is exposed from the surface of the resinlayer 4 and the metal foil 9 is formed on and integrated with the entiresurface on the other side. Furthermore, the external surface of theresin layer 4 and the exposed surface of the conductor circuit 5 are inthe same plane and the surfaces are formed into a flat state withoutunevenness. In addition, the electric components 10 connected to theconductor circuit 5 on one side of the resin layer 4 are buried in theresin layer 4. The base 6 for transcription can be released from theresin layer 4 by stripping the base 6 for transcription from the resinlayer 4 starting from an edge of the resin layer 4.

The above described heating and pressing molding is carried out in thecondition where the curing response of the resin layer 4 progresses sothat a wiring board can be gained wherein the conductor circuit 5 placedon a surface on one side of the resin layer 4 and the metal foil 9 isformed on the entire surface on the other side and wherein the electriccomponents 10 that are electrically connected to the conductor circuit 5are buried in the insulator layer that is formed of the cured resinlayer 4. The heating temperature at this time can be set at the sametemperature as in the above described cases.

In addition, in the case where the above described heating and pressingmolding can be carried out in the condition where the resin layer 4 ismaintained in the B-stage, the gained wiring board sheet 1 can beutilized for the manufacturing of a multilayer board 11 as describedbelow. The molding conditions at this time can be set at the same levelsas in the above described cases. In addition, in the case where thewiring board sheet 1 is used as the core material at the time of forminga multilayer board, the wiring board sheet can be utilized for themanufacturing of the multilayer board 11 even when the resin layer 4 isin the C-stage.

With regards to the wiring board sheet 1 h, 1 i that has been formed inthis manner, in the case where wiring board sheets 1 having resin layers4 in which electric components 10 have been buried are layered so as tobecome multilayered, metal foils 9 of the wiring board sheets 1 h, 1 iare formed as the earth layer between the layers for preventing theoccurrence of the interaction between electric components 10 in separatelayers adjacent to each other so that the electric components 10 canfunction exhibiting predetermined standard values. In addition,particularly in the case of wiring board sheets 1 i, the fluidity of theresin layers 4 b are controlled when the curing of the resin layers 4 bof the metal foil 17 with resin has been made to progress to a certainextent before the wiring board sheets are layered in the layer formingprocess so that it becomes easy to secure the dimensions between theelectric components 10 and the metal foils 9, and the distance betweenthe electric components 10 and the earth layer made of the metal foils 9can be secured at the time when the layers are formed of the abovedescribed wiring board sheets 1 in a manner where the occurrence of theinteraction between the electric components 10 in separate layersadjacent to each other can be prevented without fail. In order to makethe curing of the resin layer 4 b of a metal foil 17 with resin progressto a certain extent, this resin layer 4 b is for example, dried inadvance for approximately five minutes at 160° C.

In addition, through holes 3 filled with conductive material 2 areadditionally created in a wiring board sheet 1 as shown in FIG. 8( c) orFIG. 9( c), and thereby, a wiring board sheet 1 (wiring board sheet 1 j)can be gained. FIGS. 10( a) to 10(d) show an example of such a process.

First, as shown in FIG. 10( a), a protective film 12 is layered andplaced on a surface on one side, to which the conductor circuit 5 hasbeen transcribed, of the resin layer 4 where the conductor circuit 5 hasbeen transcribed to one surface and the metal foil 9 has been formed onthe other side of the surface. The same protective films as describedabove are used as the protective film 12.

Next, as shown in FIG. 10( b), through holes 3 are created inpredetermined positions for forming via holes of the resin layer 4 bymeans of laser processing. These through holes 3 are created so as topenetrate predetermined portions of the resin layer 4, the protectivefilm 12 and the conductor circuit 5 on one side of the resin layer 4 andso as not to penetrate the metal foil 9. At this time, the protectivefilm 12 side is irradiated with a laser beam so that the laser beam doesnot penetrate the metal foil 9 and the protective film 12 can beprevented from being released from the resin layer 4 due to the laserbeam.

After the creation of through holes 3, as shown in FIG. 10( c), throughholes 3 are filled with conductive material 2 from the external, surfaceside of the protective film 12. The above described conductive paste 8can be used as this conductive material 2. The through holes 3 arefilled in with the conductive paste 8 by applying the conductive paste 8to the external surface of the carrier base 7 so that the through holes3 are filled in with the conductive paste 8 from the openings of thethrough holes 3. At this time, the external surface of the resin layer 4is protected by the carrier base 7 so that the conductive paste 8 is notadhered to the external surface of the resin layer 4 and subsequently,as shown in FIG. 10( d), the protective film 12 where the conductivepaste 8 has been adhered to the external surface is released from theresin layer 4 side after the through holes are filled in with theconductive paste 8, and thereby, a condition is achieved where thethrough holes 3 are filled in with the conductive paste 8 and theconductive paste 8 is not adhered to the external surfaces of the resinlayer 4 and the conductor circuit 5. In addition, the conductive paste 8that has filled the through holes 3 of the protective film 12 remains,and therefore, the wiring board sheet is formed where the conductivepaste 8 protrudes outward from the through holes 3 of the resin layer 4on the surface to which the protective film 12 has been adhered (thesurface on the side where the conductor circuit 5 has been formed).

In the wiring board sheet 1 j gained in this manner, the conductorcircuit 5 is buried in a surface layer on one side of resin layer 4 sothat the conductor circuit 5 is exposed from the surface of resin layer4 and the metal foil 9 has been formed on and integrated with the entiresurface on the other side. In addition, the external surface of theresin layer 4 and the external surface of the conductor circuit 5 are inthe same plane and the surfaces are formed into a flat state withoutunevenness. Furthermore, electric components 10 connected to theconductor circuit 5 on one side of the resin layer 4 are buried in theresin layer 4. The through holes 3 are additionally created so as topenetrate the resin layer 4 and the conductor circuit 5 on one side ofthe resin layer 4 and so as not to penetrate the metal foil 9 and thesethrough holes 3 are filled with the conductive paste 8. The surface ofthis wiring board sheet 1 j on which the conductor circuit 9 has beenformed is made up of the external surface of the resin layer 4 and theexposed surface of the conductor circuit 5, which are in the same plane,and are formed into a flat state without unevenness except theprotrusions of the conductive paste 8.

Here, after the conductor circuit 5 on which the electric components 10have been mounted has been transcribed to the resin layer 4, the throughholes 3 filled with the conductive material 2 are created because theresin layer 4 is fluidized as the electric components 10 are buried inthe resin layer 4 at the time when the conductor circuit 5 on which theelectric components 10 have been mounted is transcribed to the resinlayer 4 and, in the case where the through holes 3 are created, there isa risk of the shapes of the through holes 3 being greatly deformed. Inorder to prevent such a deformation of the through holes 3 for formingthe via holes 15, the through holes 3 are created after the electriccomponents 10 have been buried in the resin layer 4.

Here, in the case where the above described heating and pressing moldingis carried out in the condition where the resin layer 4 is maintained inthe B-stage, this wiring board sheet 1 j can be utilized for themanufacturing of the multilayer board 11 as described below. The moldingcondition at this time can be set at the same levels as in the abovedescribed cases. In addition, in the case where the wiring board sheet 1j is used as the core material at the time of forming a multilayerboard, the wiring board sheet can be utilized for the manufacturing ofthe multilayer board 11 even when the resin layer 4 is in the C-stage.

In addition, through holes 3 filled with conductive material 2 andhaving hole plating 18 are created in the wiring board sheet 1 in whichno through holes 3 have been created so that a wiring board sheet 1(wiring board sheet 1 k) can be gained. FIGS. 11( a) to 11(c) show anexample of such a process.

Though in the illustrated example, the through holes 3 filled with theconductive material 2 and having the hole plating 18 are created in thewiring board sheet 1 a shown in FIG. 1( c), the invention is not limitedto such an embodiment, but rather through holes 3 filled with conductivematerial 2 and having hole plating 18 can be created, in accordance witha similar method, in any wiring board sheet 1 according to the presentinvention where no through holes 3 have been created as shown in FIGS.2( c), 4(c), 8(c), and 9(c).

First, as shown in FIG. 11( a), a protective film 12 is layered andplaced on one or two surfaces (two surfaces in the figures) to which aconductor circuit 5 of a resin layer 4 has been transcribed. Theprotective films as described above are used as the protective film 12.

Next, as shown in FIG. 11( b), through holes 3 are created inpredetermined positions for forming via holes of the resin layer 4 bymeans of laser processing. These through holes 3 are created so as topenetrate predetermined portions of the resin layer 4, the protectivefilm 12 and the conductor circuits 5 on both sides of the resin layer 4.At this time, the protective film 12 side is irradiated with the laserbeam, and thereby, the protective film 12 can be prevented from beingreleased from the resin layer 4 due to the laser beam.

After the through holes 3 have been created, the hole plating 18 isformed on the inner surfaces of the through holes 3 in the conditionwhere the protective film 12 is adhered, and then, the through holes 3are filled in with the conductive material 2 from the external surfaceside of the protective film 12. A conductive paste 8 as described abovecan be used as this conductive material 2. The through holes 3 arefilled in with the conductive paste 8 by applying the conductive paste 8to the external surface of the protective film 12 so that the throughholes 3 are filled in with the conductive paste 8 from the openings ofthe through holes 3. At this time, the external surface of the resinlayer 4 is protected by the protective film 12 so that the conductivepaste 8 is not adhered to the external surface of the resin layer 4.

Next, the protective film 12 where the conductive paste 8 has beenadhered to the external surface is released from the resin layer 4 sideas shown in FIG. 11( c) after the through holes have been filled in withthe conductive paste 8, and thereby, a condition is achieved wherein thehole plating 18 is formed inside of the through holes 3 which are filledin with the conductive paste 8 and no conductive paste 8 is adhered tothe external surface of the resin layer 4 and the conductor circuits 5.In addition, the conductive paste 8 that has filled the through holes 3of the protective film 12 remains so that the wiring board sheet isformed in a manner where the conductive paste 8 protrudes outward fromthe through holes 3 of the resin layer 4 on the surface on the side towhich the protective film 12 has been adhered (the surface on the sidewhere the conductor circuit 5 is formed).

In the wiring board sheet 1 k gained in this manner, the conductorcircuits 5 are buried in the surface layers on both sides of the resinlayer 4 so that the conductor circuits 5 are exposed from the surfacesof the resin layer 4 and electric components 10 buried in the resinlayer 4 are mounted on the conductor circuits 5 on one or both sides ofthe resin layer. In addition, the external surfaces of the resin layer 4and the exposed surfaces of the conductor circuits 5 are in the samepanes and the surfaces are formed into a flat state without unevenness.Furthermore, the through holes 3 are created so as to penetrate theresin layer 4 and the conductor circuits 5 and hole plating 18 is formedinside of these through holes 3 which are filled in with the conductivepaste 8. In particular, though the resin layer 4 incorporatingcomponents has a great thickness and in some cases, the reliability ofthe conductivity of the through holes having only the conductive paste 8becomes insufficient, a high reliability of the conductivity can begained by forming hole plating 18 even in the case of the resin layer 4having a great thickness. The surface of this wiring board sheet 1 k onwhich the conductor circuit 9 has been formed is formed of the externalsurface of the resin layer 4 and the external surface of the conductorcircuit 5, which are in the same plane, and is formed into a flat statewithout unevenness except the protrusions of the conductive paste 8.

Copper plating or the like can be formed as the above described holeplating 18 which can be formed by appropriately combining an electrolessplating treatment and an electrolytic plating treatment. In particular,in the case where the hole plating 18 is formed only in accordance withan electroless plating treatment, an increase in the thickness of thehole plating 18 can be restricted so that the hole plating 18 can beprevented from being stripped together with the plating film formed onthe protective film 12 at the time when the protective film 12 isreleased from the resin layer 4 side, and thereby, the reliability ofthe conductivity can be improved. At this time, even in the case wherethe hole plating 18 is formed into a thin film only in accordance withthe electroless plating treatment, a high reliability of theconductivity can be secured by the hole plating 18 and the conductivepaste 8 since the through holes 3 are filled in with the conductivepaste 8.

In addition, in the case where there is no risk of stripping the holeplating 18 at the time when the protective film 12 is released asdescribed above, the hole plating 18 is formed by carrying out anelectrolytic plating treatment after an electroless plating treatment,and thereby, the reliability of the conductivity in the hole plating 18can be increased. In the case where the thickness of the hole plating 18is increased by means of electroless plating and electrolytic platingtreatments in the above described manner, a resin paste 20 made of athermosetting resin composition that does not include conductive powdersuch as silver powder or copper powder is used in place of the abovedescribed conductive paste 8 in the embodiment shown in FIGS. 11( a) to11(c), and thereby, the reliability of the conductivity in the via holescan be secured only by the hole plating 18.

Here, after the conductor circuits 5 on which the electric components 10have been mounted have been transcribed to the resin layer 4, thethrough holes 3 filled in with the conductive material 2 are createdbecause the resin layer 4 is fluidized as the electric components 10 areburied in the resin layer 4 at the time when the conductor circuits 5 onwhich electric components 10 have been mounted are transcribed to theresin layer 4 and at this time, in the case where through holes 3 havebeen created, there is a risk of the shapes of the through holes 3 beinggreatly deformed. In order to prevent such a deform of the shapes of thethrough holes 3 for forming the via holes 15 as described above, thethrough holes 3 are created after the electric components 10 have beenburied in the resin layer 4.

Here, in the case where the above described heating and pressing moldingis carried out in the condition where the resin layer 4 is maintained inthe B-stage, this wiring board sheet 1 k can be utilized for themanufacturing of a multilayer board 11 as described below. The moldingconditions at this time can be set at the same levels as in the abovedescribed cases. In addition, in the case where the wiring board sheet 1k is used as the core material at the time of forming the multilayerboard, the wiring board sheet can be utilized for the manufacturing ofthe multilayer board 11 even when the resin layer 4 is in the C-sheet.

In each of the wiring board sheets 1 as described above, the conductorcircuit 5 is formed through transcription to the resin layer 4 and theelectric components 10 mounted on the conductor circuit 5 are buried andplaced in the resin layer 4 due to the fluidity of the resin layer 4 asthe resin layer is melted and softened, and therefore, the electriccomponents 10 can be placed inside the resin layer 4 in a manner wherethe fluidity of the resin layer 4 at this time prevents no air spacesfrom being generated around the electric components 10. Therefore, inthe case where the insulation layer is formed of the cured resin layer4, a wiring board can be gained where the electric components 10 areplaced inside the insulation layer so that the amounts of componentsmounted on the wiring board can be increased and the miniaturization ofthe wiring board can be achieved by restricting the protrusions of theelectric components 10 from the wiring board and in addition, there ismore freedom in the wiring design due to the expansion of the areaswhere the electric components 10 can be mounted. Furthermore, theelectric components 10 are placed inside the insulating layer withoutthe existence of air spaces around the electric components, andtherefore, no air remains around the electric components 10 so thatcracking of the insulation layer, damages to the electric components andthe occurrence of the defects, such as, a wire disconnection can berestricted even in the case where stress is received due to heat.Furthermore, the electric components 10 can be placed at arbitrarypositions due to the fluidity of the resin layer 4 that has been meltedand softened regardless of the amount of mounting or the positions ofmounting of the electric components 10 and electric components 10 can beplaced at arbitrary portions inside the resin layer 4 or inside theinsulation layer gained by curing the resin layer 4 without undergoing acomplicated process.

In addition, in order to gain a wiring board, each of the abovedescribed wiring board sheets 1 is formed in a manner where the resinlayer 4 is maintained in the B-stage and collective molding is carriedout by curing the respective resin layers in the condition where two ormore wiring board sheets 1 are layered, and thereby, the multilayerboard 11 can be gained. In addition, a wiring board sheet 1 where theresin layer 4 is in the C-stage is used as the core material on whichanother wiring board sheet 1 where the resin layer 4 is in the B-stageis layered, and then, the respective resin layer 4 are cured so that themultilayer board 11 can be gained. Furthermore, the multilayer board 11can be gained in accordance with a build-up manufacturing method whereinlayering of a wiring board sheet 1 where the resin layer 4 is maintainedin the B-stage on a wiring board sheet 1 where the resin layer 4 is inthe C-stage as well as the formation of a conductor circuit and viaholes, if necessary, are repeated.

In addition, the multilayer board 11 can be gained by using a wiringboard sheet 1 as described above and a sheet 13 having a resin layer 4where no electronic materials are buried in this resin layer 4. In thiscase, one or more wiring board sheets 1 and one or more other sheets 13having a resin layer 4 in the B-stage are layered so that collectivemolding can be carried out in this condition where the respective resinlayers are cured, and thereby, the multilayer board 11 can be gained. Inaddition, a wiring board sheet 1 where the resin layer 4 is in theC-stage or another sheet 13 is used as the core material on whichanother wiring board sheet 1 where the resin layer 4 is maintained inthe B-stage or another sheet 13 where the resin layer 4 is maintained inthe B-stage is layered, and then, the respective resin layers 4 arecured, and thereby, the multilayer board 11 can be gained. Furthermore,the multilayer board 11 can be gained in accordance with a build-upmanufacturing method wherein layering of a wiring board sheet 1 or asheet 13 where the resin layer 4 is maintained in the B-stage on awiring board sheet 1 or a sheet 13 where the resin layer 4 is maintainedin the C-stage, curing of the resin layers 4 as well as the formation ofa conductor circuit and via holes, if necessary, are repeated for theformation of a multilayer.

A known metal foil with resin, a prepreg, a resin sheet, an unclad boardor the like which are utilized at the time of the manufacture of amultilayer board can be utilized as the sheet 13 and additionally, aresin sheet where a circuit has been formed or a resin sheet where viaholes have been created can also be utilized.

In particular, in the case where a sheet where a conductor circuit 5, ametal foil 9 or through holes 3 filled with conductive material 2 areprovided to the resin layer 4 is used as the sheet 13, the formations ofan insulation layer, a conductor circuit 5, via holes and the like canbe carried out on the sheet 13. Such a sheet 13 is described below.

FIGS. 15( a) to 15(d) show the formation process for a resin layer 4that is used for the manufacture of a sheet 13 and first, as shown inFIG. 15( a), the above described resin composition is applied to onesurface of the carrier base 7 and is heated and dried so as to beconverted to the semi-cured condition (B-stage), and thus, the resinlayer 4 is formed on the surface of the carrier base 7.

The same resin composition as described above is used. In addition, asynthesized resin film such as a PET film, or a metal foil, can be usedas the carrier base 7. In the case where a metal foil is used, it ispreferable for the surface on which the resin layer 4 is formed a mirrorsurface in order to enhance the release properties at the time when thecarrier base 7 is released from the resin layer 4. A material thatallows the creation of through holes 3 at the time of laser processingis selected for such a metal foil and it is preferable to use a rolledcopper foil, an electrolytic copper foil, an aluminum foil, a metalalloy foil, a metal clad foil or the like.

The heating and drying conditions at this time can be set at the samelevels as in the case of the formation of a resin sheet 4 a. Inaddition, it is preferable for the resin layer 4 to have a thickness inthe range of 50 μm to 300 μm.

Laser processing is carried out on the resin layer 4 that has beenformed as described above by irradiating the resin layer with a laserbeam such as a YAG laser or a carbonic acid gas laser in the conditionwhere the resin layer is supported by the carrier base 7, and thereby,through holes 3 are created at predetermined positions for forming viaholes 15 as shown in FIG. 15( b). These through holes 3 are created soas to penetrate both the resin layer 4 and the carrier base 7 and atthis time, in the case where the carrier base 7 side is irradiated withthe laser beam, the resin layer 4 can be prevented from being releasedfrom the layer of the carrier base 7.

After the creation of through holes 3, the through holes 3 are filled inwith conductive material 2 from the external surface side of the carrierbase 7 as shown in FIG. 15( c). A conductive paste 8 as described abovecan be used as this conductive material 2. The through holes 3 arefilled in with the conductive paste 8 by applying the conductive paste 8to the external surface the carrier base 7 so that the through holes 3are filled in with the conductive paste 8 from the openings of thethrough holes 3. At this time, the external surface of the resin layer 4is protected by the carrier base 7 so that no conductive paste 8 isadhered to the external surface of the resin layer 4 and subsequently,the carrier base 7 where the conductive paste 8 has been adhered to theexternal surface is released from the resin layer 4 as shown in FIG. 15(d) after the through holes have been filled in with the conductive paste8, and thereby, a condition is achieved wherein the through holes 3 arefilled in with the conductive paste 8 and no conductive paste 8 isadhered to the external surface of the resin layer 4. In addition, theconductive paste 8 that has been filled in the through holes 3 of thecarrier base 7 remains so that the sheet is formed where the conductivepaste 8 protrudes outward from the through holes 3 of the resin layer 4on the side to which the carrier base 7 has been adhered.

As a result of this, a sheet 13 (sheet 13 f) having through holes 3filled with conductive material 2 is gained.

In addition, a resin layer formed by impregnating an unwoven cloth witha resin composition in slurry form, which is then dried, can be used asthe resin layer 4. An appropriate glass unwoven cloth, an organic fiberunwoven cloth or the like can be used as the unwoven cloth. In the casewhere the resin layer 4 that has been formed in this manner is used, aprotective film 12 is adhered to one surface of the resin layer 4 inplace of the carrier base 7 in FIGS. 15( a) to 15(d) while the otherparts are made to remain the same as described above, and thereby, thesheet 13 (sheet 13 f) having the through holes 3 filled with theconductive material 2 is gained.

The through holes 3 filled with the conductive material 2 in this sheet13 f are created as vias (via holes) for electrically connecting theconductor circuits 5 on both sides of resin layer 4 at the time ofmanufacturing of a multilayer board. Here, the resin layer 4 of thesheet 13 f is in the B-stage, and therefore, is easily compressed whenbeing layered at the time of the manufacturing of a multilayer board sothat the through holes 3 are filled with the conductive material 2 (theconductive paste 8), which is compressed, and a sufficient electricconnection vis-à-vis the conductor circuits 5 on both sides of the resinlayer can be secured, wherein a high reliability of the conductivity canbe maintained.

The above described sheet 13 is formed so that the resin layer 4 is inthe B-stage while the resin layer 4 may be in the C-stage in the casewhere this sheet 13 is used as the core material at the time of themanufacturing of the multilayer board 11.

No electronic elements 10 are buried in the resin layer 4 of this sheet13 so that the resin layer 4 can be formed to have a small thickness,and therefore, the conductance between the layers can be secured only bymeans of the conductive past 8 without forming the hole plating 18inside the through holes 3 for forming vias. Here, hole plating can beformed on the inner surfaces of the through holes 3 prior to the fillingof the through holes 3 with the conductive material 2 (the conductivepaste 8).

In addition, in the case where the resin layer 4 is particularly in theC-stage, in order to secure the reliability of the conductivity, thehole plating 18 is carried out on the inner surfaces of the throughholes 3 after the through holes 3 have been created as FIG. 15( b) and,subsequently, the through holes 3 are filled in with the conductivematerial 2 (the conductive paste 8) as shown in FIG. 15( c) so that thesheet 13 f shown in FIG. 15( d) can be gained.

In addition, the sheet 13 f having the through holes 3 filled with theconductive material 2 as described above and the base 6 fortranscription where the conductor circuit 5, to be later transcribed, isformed on a surface are used so that the conductor circuit 5 istranscribed to the resin layer 4 of the sheet 13 f from the base 6 fortranscription, and thereby, the sheet 13 where the conductor circuit 5is formed on one side (sheet 13 a with a circuit on one side) can begained.

FIGS. 16( a) to 16(c) show an example of a manufacturing process for asheet 13 a with a circuit on one side. First, as shown in FIGS. 16( a)and 16(b), a base 6 for transcription on which a conductor circuit 5 hasbeen formed is layered and placed on one surface of a sheet 13 f made ofa resin layer 4 having through holes 3 filled with conductive material 2so that the surface on which the conductor circuit has been formed isopposite to the resin layer 4 in a condition where the positions of thethrough holes 3 and the conductor circuit 5 are adjusted, and then,heating and pressing molding is carried out so that the sheet and thebase for transcription are integrated. At this time, the conductorcircuit 5 and the through holes 3 are positioned so that predeterminedportions of the conductor circuit 5 are placed on the positions of theopenings of the through holes 3.

A base for transcription that has been formed as described above is usedfor the base 6 for transcription on which the conductor circuit 5 hasbeen formed. At this time, the base 6 for transcription may be formed ofa metal material such as stainless steal in the same manner as the basefor transcription that is used for the manufacturing of the wiring boardsheet 1, or the base 6 for transcription can be formed of a resin film.That is to say, particularly in the case where a conductor circuit 5, tobe later transcribed, is formed on the base 6 for transcription, andelectric components 10 are mounted at the time of the manufacturing ofthe wiring board sheet 1, the temperature of the base 6 fortranscription becomes very high due to the soldering processing at thetime of mounting of the electric components 10, and sometimes it becomesnecessary to apply a large amount of heat to the resin layer 4 in orderto sufficiently melt and soften the resin layer 4 at the time when theelectric components 10 are buried in the resin layer 4, and therefore, ahigh resistance to heat is required for the base 6 for transcription.However, the electric components 10 are not mounted on the base 6 fortranscription at the time when the sheet 13 is formed, and therefore, aresistance to heat that is not as high as that of the time ofmanufacture of the wiring board sheet 1 is required at the time when thesheet 13 is formed because the electric components 10 are not mounted onthe base 6 for transcription, and as a result, the base 6 fortranscription can be formed of a resin film. In this case, a resin filmsuch as a known PET film or a fluoride based film that has an adhesiveallowing release from the conductor circuit 5 by means of heatapplication or UV light application can be used.

This heating and pressing molding is carried out in a condition wherethe resin layer 4, after being formed, is maintained in the B-stage, ina condition where the resin layer 4 is in the C-stage, or preferably ina condition where the conductive paste 8 that has filled the throughholes 3 is maintained in the B-stage.

In this molding process, the resin layer 4 is melted and softened so asto be fluidized, and thereby, the conductor circuit 5 formed on the base6 for transcription is buried in the resin layer 4. In addition, at thistime, predetermined portions of the conductor circuit 5 for creating thethrough holes 3 are buried in the resin layer 4, and thereby, areelectrically connected to the conductive paste 8 that has filled thethrough holes 3. In addition, the portions of the conductive paste 8that protrude from the through holes 3 are pressed into the throughholes 3 by applying pressure and the predetermined portions of theconductor circuit 5 for the creation of the through holes 3 are furtherpressed so as to be buried in the resin layer 4, and are furthercompressed within the through holes 3. As a result of this, theconductivity of the conductive layers within the through holes 3 formedof the conductive paste 8 increases so as to enhance the reliability ofthe connection between the conductor circuits 5 through the via holes atthe time of the manufacturing of the multilayer board 11.

It is preferable to carry out the above described heating and pressingmolding of the sheet 13 a with a circuit on one side under reducedpressure or in a vacuum, and in such cases, it becomes difficult forvoids to be included inside the sheet, increasing the reliability. Inaddition, in the case where this heating and pressing molding is carriedout in a condition where the curing response of the resin layer 4 andthe conductive paste 8 does not progress in a manner where the resinlayer 4 and the conductive paste 8 within the through holes 3 afterbeing formed are maintained in the B-stage, it is preferable to heat ata temperature of 100° C. to 140° C. for approximately 10 minutes thoughthese conditions depend on the makeup of the resin composition thatforms the resin layer 4 and depend on the makeup of the conductive paste8. In addition, it is necessary to set the pressure at the time of themolding in accordance with the fluidity of the resin layer 4 when beingmelted and softened, and for example, in the case where the fluiditywhen melted and softened is high, an easy molding is possible by meansof a vacuum laminator while in the case where the fluidity when meltedand softened is low, the molding can be carried out by a applyingpressure to approximately 2.94 MPa (30 kgf/cm2).

Next, as shown in FIG. 16( c), the base 6 for transcription is releasedfrom the resin layer 4 while the conductor circuit 5 is made to remainin the resin layer 4, and thereby, a sheet 13 a with a circuit on oneside is gained. This sheet 13 a with a circuit on one side is formed ina manner where the conductor circuit 5 is buried in a surface layer onone side of the resin layer for in the B-stage or in the C-stage havingthrough holes 3 filled with conductive material 2 so that the conductorcircuit 5 is exposed from the surface of the resin layer 4, and theexternal surface of the resin layer 4 and the exposed surface of theconductor circuit 5 are in the same plane where the surfaces are formedinto a flat state without unevenness.

The base 6 for transcription can be released from the resin layer 4 bystripping the base 6 for transcription from the resin layer 4 startingfrom an edge of the resin layer 4. At this time, in the case wherestainless steal having a thickness of 50 μm to 200 μm, in particular athickness of 100 μm, is used, the base 6 for transcription has a hightenacity and an appropriate flexibility so that the base 6 fortranscription can be easily released from the resin layer 4, which doesnot bend, due to the flexibility of the base 6 for transcription, andthus, it is easy to handle the base 6 for transcription. The base 6 fortranscription, after being released in this manner, can be utilized forthe manufacturing of a sheet 13 a with a circuit on one side by forminga conductor circuit 5 again on the base 6 for transcription after beingcleaned by means of degreasing.

In addition, a sheet 13 f made of a resin layer 4 having through holes 3filled with conductive material 2 as described above, and a base 6 fortranscription where a conductor circuit 5, to be later transcribed, isformed on a surface are used so that the conductor circuit 5 istranscribed from the base 6 for transcription to the resin layer 4, andthereby, a sheet 13 where the conductor circuits 5 are formed on the twosurfaces (sheet 13 b with circuits on both sides) can be gained.

FIGS. 17( a) to 17(c) show an example of a manufacturing process for asheet 13 b with circuits on both sides. First, as shown in FIGS. 17( a)and 17(b), the bases 6 for transcription where the conductor circuits 5have been formed as described above are respectively layered and placedon both sides of the sheet 13 f made of the resin layer 4 having thethrough holes 3 filled with conductive material 2 so that the surfaceson which the conductor circuits have been formed are opposite to theresin layer 4 in the condition where the positions of the through holes3 and the conductor circuits 5 are adjusted, and then, heating andpressing molding is carried out in the same conditions as in themanufacturing of the above described sheet 13 a with a circuit on oneside; and thereby, the bases for transcription and the resin layer areintegrated; and at this time, the conductor circuits 5 and the throughholes 3 are positioned so that the predetermined portions of theconductor circuit 5 are placed on the positions of the openings of thethrough holes 3. This heating and pressing molding is carried out in acondition where the resin layer 4 after being formed is maintained inthe B-stage, in a condition where the resin layer 4 is in the C-stage,or preferably in a condition where the conductive paste 8 within thethrough holes 3 is maintained in the B-stage.

In this molding process, the resin layer 4 is melted and softened so asto be fluidized so that the conductor circuits 5 formed on the bases 6for transcription are buried in the resin layer 4. In addition, at thistime, predetermined portions of conductor circuit 5 are buried in theresin layer 4 at the positions for the creation of through holes 3, andthereby, are electrically connected to the conductive paste 8 that hasfilled the through holes 3. In addition, the portions of the conductivepaste 8 protruding from the through holes 3 are pushed into throughholes 3 by applying pressure and predetermined portions of the conductorcircuits 5 are buried in the resin layer 4 from both sides of thethrough holes 3 so as to be further pushed into the through holes 3 sothat the conductive paste 8 is compressed within the through holes 3,and thereby, the conductivity of the conductive layers within thethrough holes 3 formed of the conductive paste 8 is increased, enhancingthe reliability of the connection between the conductor circuits 5through the via holes at the time of the manufacturing of the multilayerboard 11.

Next, as shown in FIG. 17( c), the bases 6 for transcription arereleased from the resin layer 4 while the conductor circuits 5 are madeto remain in the resin layer 4, and thereby, a sheet 13 b with circuitson both sides is gained. This sheet 13 b with circuits on both sides isformed in a manner where the conductor circuits 5 are buried in thesurface layers on both sides of the resin layer 4 in the B-stage or inthe C-stage having the through holes 3 filled with conductive material 2so that the conductor circuits 5 are exposed from the surfaces of theresin layer 4 where the external surface of the resin layer 4 and theexposed surface of the conductor circuits 5 are in the same plane andthe surfaces are formed into a flat state without unevenness.

According to the manufacturing process for a sheet 13 (sheet 13 c with ametal foil) shown in FIG. 18, a sheet 13 f made of the resin layer 4having the through holes 3 filled with conductive material 2 asdescribed above and a metal foil 9 are used so as to gain a sheet 13 cwith a metal foil where the metal foil 9 is placed on one surface of theresin layer 4.

Here, the metal foil 9 is layered and placed on one side of the sheet 13f made of the resin layer 4 having the through holes 3 filled with theconductive material 2 so as to be opposite to the resin layer 4, andthen, heating and pressing molding is carried out in the same conditionsas in the above described cases so that the metal foil and the sheet areintegrated. This heating and pressing molding is carried out in acondition where the resin layer 4 after being formed is maintained inthe B-stage, in a condition where the resin layer 4 is in the C-stage,or preferably in a condition where the conductive paste 8 within thethrough holes 3 is also maintained in the B-stage.

The metal foils as described above can be used as the metal foil 9. Inaddition, it is preferable for the surface of this metal foil 9 on whichthe resin layer 4 is formed to be a rough surface in order to ensure theadhesiveness vis-à-vis the resin layer 4. In the case where anelectrolytic copper foil is used as the metal foil 9, for example, theresin layer 4 can be formed on the rough surface that has originallybeen formed on the electrolytic copper foil. In addition, a surfacetreatment can be carried out on the metal foil 9 and a surfaceroughening treatment by means of, for example, a blackening treatment oran alumite treatment can be cited as this surface treatment.

In this molding process, the metal foil 9 is electrically connected tothe conductive paste 8 that has filled the through holes 3. In addition,the portions of the conductive paste 8 protruding from the through holes3 are pressed into the through holes 3 by a applying pressure so as tobe compressed within the through holes 3, and thereby, the conductivityof the conductive layers within the through holes 3 formed of theconductive paste 8 is increased, enhancing the reliability of theconnection between the conductor circuits 5 through via holes 15 at thetime of the manufacturing of the multilayer board 11.

FIGS. 19( a) to 19(c) show another example of a manufacturing processfor a sheet 13. This sheet 13 (sheet 13 d with a metal foil and acircuit) is formed in a manner where a resin layer 4 in the B-stage orin the C-stage is formed on one surface of a metal foil 9 andfurthermore a conductor circuit 5 is transcribed to this resin layer 4.

First, the resin layer 4 in the B-stage is formed on a surface of themetal foil 9. This resin layer 4 is formed by a applying the same resincomposition as described above to the metal foil 9, which is then heatedand dried.

The same metal foils as described above can be used as the metal foil 9and it is preferable for the surface on which the resin layer 4 isformed to be a rough surface in order to ensure the adhesivenessvis-à-vis the resin layer 4. In the case where an electrolytic copperfoil is used as the metal foil 9, for example, the resin layer 4 can beformed on the rough surface that has originally been formed on theelectrolytic copper foil. In addition, a surface treatment can becarried out on the metal foil 9 and a surface roughening treatment bymeans of, for example, a blackening treatment or an alumite treatmentcan be cited as this surface treatment. Furthermore, it is preferablefor this metal foil 9 to have a thickness of 10 μm to 150 μm. Inaddition, it is preferable for the thickness of the resin layer 4 to be50 μm to 300 μm.

Next, the conductor circuit 5 is transcribed to the resin layer 4 fromthe base 6 for transcription by using the base 6 for transcription wherethe conductor circuit 5, to be later transcribed, is formed on thesurface as described above. At this time, as shown in FIGS. 19( a) and19(b), the base 6 for transcription on which the conductor circuit 5 hasbeen formed is layered and placed on one surface (surface on the side onwhich the metal foil 9 is not placed) of the resin layer 4 so that thesurface on which the conductor circuit 5 has been formed is opposite tothe resin layer 4, and then, heating and pressing molding is carried outso that the base for transcription and the resin layer are integrated.This heating and pressing molding is carried out in a condition wherethe resin layer 4, after being formed, is maintained in the B-stage orin a condition where resin layer 4 is in the C-stage.

In this molding process, the resin layer 4 is melted and softened so asto be fluidized and the conductor circuit 5 formed on the base 6 fortranscription is buried in the resin layer 4.

Next, as shown in 19(c), the resin layer 4 is released from the base 6for transcription while the conductor circuit 5 is made to remain in theresin layer 4, and thereby, a sheet 13 d with a metal foil and a circuitis gained. This sheet 13 d with a metal foil and a circuit is formed ina manner where the conductor circuit 5 is buried in a surface layer ofthe resin layer 4 in the B-stage or in the C-stage so that the conductorcircuit 5 is exposed from the surface of the resin layer 4 where theexternal surface of the resin layer 4 and the exposed surface of theconductor circuit 5 are in the same plane and the surfaces are formedinto a flat state without unevenness.

In the manufacturing process for a sheet 13 (sheet 13 e with a metalfoil and a circuit) shown in FIGS. 20( a) to 20(e) and 21(a) to 21(c),first, after the resin layer 4 has been formed on the surface of themetal foil 9 in the same manner as in the above described cases, asdescribed in FIG. 20( b), a protective film 12 is placed on a surface ofthe resin layer 4 on the side opposite to the side where the metal foil9 has been placed before the conductor circuit 5 is formed. The sameprotective films as described above can be used as the protective film12.

Next, as shown in FIG. 20( c), through holes 3 are created inpredetermined positions of the resin layer 4 for forming via holes 15 bymeans of laser processing. These through holes 3 are created so as topenetrate both the resin layer 4 and the protective film 12. At thistime, the protective film 12 side is irradiated with a laser beam, andthereby, the resin layer 4 can be prevented from being released from thelayer of the protective film 12. In addition, the resin layer isirradiated with the laser beam in a condition where no openings arecreated in the metal foil 9.

After the through holes 3 have been created, as shown in FIG. 20( d),the through holes 3 are filled in with conductive material 2 from theexternal surface side of the protective film 12. Hole plating may beformed on the inner surfaces of the through holes 3 prior to the fillingof the through holes with conductive material 2. The conductive paste 8,similar to those in the above described cases, can be used as thisconductive material 2. The through holes 3 are filled in with theconductive paste 8 from the openings of the through holes 3 by applyingthe conductive paste 8 to the external surface of the protective film12. At this time, the external surface of the resin layer 4 is protectedby the protective film 12 so that no conductive paste 8 is adhered tothe external surface of the resin layer 4.

Next, after the through holes have been filled in with the conductivepaste 8, as shown in FIG. 20( e), the protective film 12 where theconductive paste 8 has been attached to the external surface is releasedfrom the resin layer 4, and thereby, a condition is achieved wherein thethrough holes 3 of the resin layer 4 are filled in with the conductivepaste 8 and no conductive paste 8 is adhered to the external surface ofthe resin layer 4. In addition, the conductive paste 8 that has filledthe through holes 3 of the protective film 12 remains so that theconductive paste 8 protrudes outward from the through holes 3 of theresin layer 4 on the surface of the side where the protective film 12has been adhered.

Next, as shown in FIGS. 21( a) to 21(c), a base 6 for transcriptionwhere a conductor circuit 5, to be later transcribed, has been formed ona surface as described above, is used so that the conductor circuit 5 istranscribed to the resin layer 4 from the base 6 for transcription. Atthis time, as shown in FIGS. 21( a) and 21(b), the base 6 fortranscription on which the conductor circuit 5 has been formed asdescribed above is layered and placed on one surface (surface on theside where the metal foil 9 is not placed) of the resin layer 4, havingthe through holes 3 filled with conductive material 2 so that thesurface on which the conductor circuit 5 has been formed is opposite tothe resin layer 4 in the condition where the positions of the throughholes 3 and of the conductor circuit 5 are adjusted, and then, heatingand pressing molding is carried out in the same conditions as in theabove described cases so that the base for transcription and the resinlayer are integrated. At this time, the conductor circuit 5 and thethrough holes 3 are positioned so that the predetermined portions of theconductor circuit 5 are placed on the positions of the openings of thethrough holes 3. This heating and pressing molding is carried out in acondition where the resin layer 4 after being formed is maintained inthe B-stage, in a condition where the resin layer 4 is in the C-stage orpreferably in a condition where the conductive paste 8 within thethrough holes is maintained in the B-stage.

In this molding process, the resin layer 4 is melted and softened so asto be fluidized and the conductor circuit 5 formed on the base 6 fortranscription is buried in the resin layer 4. In addition, at this time,predetermined portions of the conductor circuit 5 are buried in theresin layer 4 in positions for the creation of through holes 3, andthereby, are electrically connected to the conductive paste 8 that hasfilled the through holes 3. In addition, the portions of the conductivepaste 8 protruding from the through holes 3 are pressed into the throughholes 3 by applying pressure and predetermined portions of the conductorcircuit 5 are buried in the resin layer 4 in positions for the creationof the through holes 3, and thereby, the predetermined portions of theconductor circuit 5 are further pressed into the through holes 3 so asto be compressed in the through holes 3. As a result of this, theconductivity of the conductive layers within the through holes 3 formedof the conductive paste 8 is increased, enhancing the reliability of theconnection between the conductor circuits 5 through via holes 15 at thetime of the manufacturing of the multilayer board 11.

Next, as shown in FIG. 21( c), the base 6 for transcription is releasedfrom the resin layer 4 while the conductor circuit 5 is made to remainin the resin layer 4, and thereby, a sheet 13 e with a metal foil and acircuit is gained. This sheet 13 e with a metal foil and a circuit isformed in a manner where the conductor circuit 5 is buried in a surfacelayer of the resin layer 4 in the B-stage or in the C-stage having thethrough holes filled with conductive material 2 so that the conductorcircuit 5 is exposed from the surface of the resin layer 4 where theexternal surface of the resin layer 4 and the exposed surface of theconductor circuit 5 are in the same plane and the surfaces are formedinto a flat state without unevenness.

Though a concrete manufacturing process for a multilayer board 11, usinga wiring board sheet 1 and a sheet 13 as described above, is shown inthe following, the multilayer board 11 according to the presentinvention is not limited to the multilayer board manufactured inaccordance with the following process, but rather a multilayer boardhaving a variety of configurations can be gained by appropriatelycombining two or more wiring board sheets 1, or at least one wiringboard sheet 1 and another sheet 13 as described above, so as to form anintegrated multilayer. At this time, wiring board sheets 1 and othersheets 13 can be layered in a manner where the surface on which theconductor circuit 5 or the metal foil 9 is formed, is opposite to thesurface on which the metal foil 9 or the conductor circuit 5 is formed,the surface on which the openings of the through holes 3 are created, orthe surface on which neither the metal foil 9 or the conductor circuit 5have been formed.

In an example shown in FIGS. 22( a) to 22(c), one wiring board sheet 1 dgained in accordance with the process shown in FIGS. 4( a) to 4(c), onewiring board sheet 1 e, gained in the accordance with the process shownin FIGS. 5( a) to 5(d), and one sheet 13 c with a metal foil gained inaccordance with the process shown in FIGS. 18( a) and 18(b), are used sothat these sheets are layered and integrated.

In an example shown in FIGS. 22( a) to 22(c), first, the wiring boardsheet 1 e, the wiring board sheet 1 d and the sheet 13 c with a metalfoil are layered and placed on each other in the condition where thesurface of the wiring board sheet 1 e, on which the conductor circuit 5has been formed, and the surface of the wiring board sheet 1 d, on whichthe conductor circuit 5 has not been formed, are opposite to each other,and the surface of the wiring board sheet 1 d, on which the conductorcircuit 5 has not been formed, and the surface of the sheet 13 c with ametal foil, on which the metal foil 9 has not been placed, are oppositeto each other. At this time, the respective opposite surfaces arepositioned so that predetermined portions of the conductor circuits 5are placed on the positions of the openings of the through holes 3.

Heating and pressing molding is carried out in this condition, andthereby, the wiring board sheets 1 d, 1 e, and the sheet 13 c with ametal foil are collectively layered and integrated.

In this molding process, the resin layer 4 in the B-stage is cured afterbeing melted, and thereby, the interfaces between the wiring boardsheets 1 e and 1 d and between the wiring board sheet 1 d and the sheet13 c with a metal foil are joined so that these sheets are layered andintegrated, and insulation layers 16 are formed from the cured resinlayers 4. In addition, conductive layers are formed of the curedconductive paste 8 in the through holes 3 filled with the conductivepaste 8, and thereby, via holes 15 are formed so as to electricallyconnect the conductor circuits 5, and so as to electrically connect themetal foil 9 and the conductor circuit 5. At this time, the conductivepaste 8 that has filled the through holes 3 of the sheet 1 e haselectrically connected the conductor circuit 5 and the metal foil 9 inadvance, as described above, and the conductive paste 8 is cured in thiscondition so as to form conductive layers, and thereby, via holes 15 areformed. In addition, the predetermined portions of the conductor circuit5 of the sheet 1 c are connected to the conductive paste 8 that hasfilled the through holes 3 of the sheet 1 d in the interface between thesheets 1 c and 1 d at the time when the above described integration iscarried out, and thereby, this conductive paste 8 electrically connectsthe conductor circuits 5, and the conductive paste 8 is cured in thiscondition so as to form conductive layers, and thereby, via holes 15 areformed. Furthermore, predetermined portions of the conductor circuit 5of the sheet 1 d are connected to the conductive paste 8 that has filledthe through holes 3 of the sheet 13 c with a metal foil, at the timewhen the above described integration is carried out, in the interfacebetween the sheet 1 d and the sheet 13 c with a metal foil, and thereby,this conductive paste 8 connects the conductor circuit 5 and the metalfoil 9 and the conductive paste 8 is cured in this condition so as toform the conductive layer, and thus, via holes 15 are formed.

At this time, the conductive paste 8 has been compressed in the throughholes 3 of the wiring board sheet 1 e and of the sheet 13 c with a metalfoil, in advance, as described above. Via holes 15 having a highconductivity and highly reliable connections are formed. In addition,the conductive paste 8 protruding from the openings of the through holes3 in the wiring board sheet 1 d, and these protruding portions of theconductive paste 8 are pressed into the through holes 3 by applyingpressure at the time of the above described integration so as to becompressed, and thereby, via holes 15, having a high conductivity andhighly reliable connections, are formed.

This heating and pressing molding is carried out in a condition wherethe curing response of the resin layer 4 in the B-stage and of theconductive paste 8 progresses, and though this condition depends on themakeup of the resin composition that forms the resin layer 4, it ispreferable to carry out the molding for 60 to 90 minutes under thecondition where the heating temperature is 160° C. to 185° C. and theapplied pressure is 0.3 MPa to 5 MPa. In the multilayer board 11 thathas been gained in such a manner, as shown in FIG. 22( b), metal foils 9are placed on the outermost layers on both sides of the multilayerboard, and a two-layered conductor circuit 5 is placed inside themultilayer board where via holes 15 are formed so as to electricallyconnect the respective layers. In addition, electric components 10 areplaced inside the two layers from among the three insulation layers 16.

Furthermore, an etching treatment is carried out on the metal foils 9 onthe external surfaces so as to form the conductor circuits 5 on therespective external layers on both sides of the multilayer board, andthereby, as shown in FIG. 22( c), a multilayer board 11, having afour-layered conductor circuit 5, can be gained.

In an example shown in FIGS. 23( a) to 23(c), one wiring board sheet 1 fgained in accordance with the process shown in FIGS. 7( a) and 7(b), onesheet 13 a with a circuit on one side that is gained in accordance withthe process shown in FIGS. 16( a) to 16(c), and one sheet 13 c with ametal foil that is gained in accordance with the process shown in FIGS.18( a) and 18(b) are used and these sheets are layered and integrated.

In the example shown in FIGS. 23( a) to 23(c), a condition is achievedwhere the surface of the sheet 13 c with a metal foil on which the metalfoil 9 has not been formed, and one surface of the wiring board sheet 1f (surface on which a conductor circuit 5, on which no electriccomponents 10 have been mounted, has been formed) are opposite to eachother, and the other surface of the wiring board sheet 1 f (the surfaceon which a conductor circuit 5, on which electric components 10 havebeen mounted, has been formed) and the surface of the sheet 13 a, with acircuit on one side on which no conductor circuit 5 has been formed, areopposite to each other, and these sheets are layered. At this time, therespective surfaces that are opposite to each other are positioned sothat the predetermined portions of the conductor circuits 5 are placedon the positions of the openings of the through holes 3.

Heating and pressing molding is carried out in this condition, andthereby, the wiring board sheet 1 f, the sheet 13 a with a circuit onone side, and the sheet 13 c with a metal foil, are collectivelylayered.

In this molding process, the resin layer 4 in the B-stage is cured afterbeing melted, and thereby, the interfaces between the sheet 13 c with ametal foil and the wiring board sheet 1 f, and between the wiring boardsheet 1 f and the sheet 13 a with a circuit on one side, are joined, sothat these sheets are layered and integrated where the insulation layers16 are formed of the cured resin layers 4. In addition, the conductivepaste 8 is cured to form the conductive layers in the through holes 3filled with the conductive paste 8, and thereby, via holes 15, forelectrically connecting the conductor circuits 5, and for electricallyconnecting the metal foil 9 to the conductor circuit 5, are formed. Atthis time, the conductive paste 8, that has filled the through holes 3of the sheet 1 f, has connected the conductor circuits 5 in advance, asdescribed above, and the conductive paste 8, is cured in this conditionso as to form the conductive layers, and thus, the via holes 15 areformed. In addition, in the interface between the wiring board sheet 1 fand the sheet 13 c with a metal foil, predetermined portions of theconductor circuit 5 of the wiring board sheet 1 f are connected to theconductive paste 8 that has filled the through holes 3 of the sheet 13 cwith a metal foil at the time of the above described integration, andthereby, this conductive paste 8 connects the conductor circuits 5, andthe conductive paste 8 is cured in this condition so as to form theconductive layers, and thus, the via holes 15 are formed. Furthermore,in the interface between the wiring board sheet 1 f and the sheet 13 awith a circuit on one side, predetermined portions of the conductorcircuit 5 of the wiring board sheet 1 f are connected to the conductivepaste 8, that has filled the through holes 3 of the sheet 13 a with acircuit on one side, at the time of the above described integration, andthereby, this conductive paste 8 connects the conductor circuit 5 andthe metal foil 9, so that the conductive paste 8 is cured in thiscondition so as to form the conductive layers, and thus, the via holes15 are formed.

In addition, at this time, the through holes 3 of the wiring board sheet1 f, the sheet 13 a with a circuit on one side, and the sheet 13 c witha metal foil, have been filled in with the conductive paste 8 in ahighly compressed manner, in advance, as described above, and therefore,via holes 15, having a high conductivity and highly reliableconnections, are formed.

This heating and pressing molding is carried out in a condition wherethe curing response of the resin layer 4 in the B-stage and of theconductive paste 8 progresses, and this condition can be set at the samelevels as in the above described cases.

In the multilayer board 11 gained in the above described manner, asshown in FIG. 23( b), the metal foil 9 is placed on one of the outermostlayers, and the conductor circuit 5 is placed on the other outermostlayer while the two-layered conductor circuit 5 is placed inside themultilayer board and the via holes 15 for electrically connecting therespective layers are formed. In addition, the electric components 10are placed inside one layer from among the three insulation layers 16.

In addition, an etching treatment can be carried out on the metal foils9 on the external surfaces so that conductor circuits 5 are formed onthe external layers on both sides of the multilayer board, and amultilayer board 11 having a 4-layered conductor circuit 5 can be gainedas shown in FIG. 23( c).

In an example shown in FIGS. 24( a) and 24(b), two wiring board sheets 1d gained in accordance with the process shown in FIG. 5( a) to 5(d), andone wiring board sheet 1 f gained in accordance with the process shownin FIGS. 7( a) and 7(b), are layered and integrated.

In the example shown in FIGS. 24( a) and 24(b), first, a condition isachieved where the surface of one of the wiring board sheets 1 d onwhich the conductor circuit 5 has not been formed, and the surface ofthe wiring board sheet 1 f (the surface on which the conductor circuit5, on which the electric components 10 have not been mounted, has beenmounted) are opposite to each other, and the other surface of the wiringboard sheet 1 f (the surface on which the conductor circuit 5, on whichthe electric components 10 have been mounted, has been formed) and thesurface of the other wiring board sheet 1 d, on which the conductorcircuit 5 has not been formed, are opposite to each other, and then,these sheets are layered. At this time, on the respective surfaces thatare opposite to each other, predetermined portions of the conductorcircuits 5 are positioned so as to be placed on the positions of theopenings of the through holes 3.

Heating and pressing molding is carried out in this condition, andthereby, the two wiring board sheets 1 d and the one wiring board sheet1 f are collectively layered and integrated.

In this molding process, the resin layer 4 in the B-stage is cured afterbeing melted, and thereby, the interfaces between one of the wiringboard sheets 1 d and the wiring board sheet 1 f, and between the wiringboard sheet 1 f and the other wiring board sheet 1 d, are joined, sothat these sheets are layered and integrated, and the insulation layers16 are formed of the cured resin layers 4. In addition, the conductivelayers are formed of the cured conductive paste 8 in the through holes 3filled with the conductive paste 8, and thereby, via holes 15, forelectrically connecting the conductor circuits 5, are formed. At thistime, the conductive paste 8, that has filled the through holes 3 of thewiring board sheet 1 f, has connected the conductor circuits 5, inadvance, as described above, and the conductive paste 8 is cured in thiscondition so as to form the conductive layers, and thus, via holes areformed. In addition, in the respective interfaces between the wiringboard sheet 1 f and the wiring board sheets 1 d, predetermined portionsof the conductor circuit 5 of the wiring board sheet 1 f are connectedto the conductive paste 8 that has filled the through holes 3 of thewiring board sheets 1 d at the time of the above described integration,and thereby, this conductive paste 8 connects the conductor circuits 5,and the conductive paste 8 is cured in this condition so as to form theconductive layers, and thus, the via holes 15 are formed.

In addition, at this time, the through holes 3 of the wiring board sheet1 f have been filled with the conductive paste 8 in advance, asdescribed above, and therefore, via holes 15, having a high conductivityand highly reliable connections, are formed. Furthermore, the conductivepaste 8 protrudes from the openings of the through holes 3 in the wiringboard sheets 1 d, and these protruding portions of the conductive paste8 are pressed into the through holes 3, by applying pressure at the timeof the above described collective integration, so that the conductivepaste is compressed, and thereby, via holes 15, having a highconductivity and highly reliable connections, are formed.

This heating and pressing molding is carried out in a condition wherethe curing response of the resin layer 4 in the B-stage and of theconductive paste 8 progresses, and this condition can be set at the samelevels as in the above described cases.

In the multilayer board 11 that is gained in such a manner, as shown inFIG. 24( b), the conductor circuits 5 are placed on the outermost layerson both sides of the multilayer board, and a two-layered conductorcircuit 5 is placed inside the multilayer board, and in addition, viaholes 15 for electrically connecting the respective layers are formed.Furthermore, the electric components 10 are placed inside all of thethree insulation layers 16.

In an example shown in FIGS. 25( a) and 25(b), one wiring board sheet 1b, gained in accordance with the process shown in FIGS. 3( a) to 3(d),one wiring board sheet 1 d, gained in accordance with the process shownin FIGS. 5( a) to 5(d), and one sheet 13 a with a circuit on one side,gained in accordance with the process shown in FIGS. 16( a) to 16(c),are used and these sheets are layered and integrated.

In the example shown in FIGS. 25( a) and 25(b), first, a condition isachieved where the surface of the wiring board sheet 1 d, on which theconductor circuit 5 has not been formed, and one surface of the wiringboard sheet 1 b (the surface where the conductive paste 8 protrudes fromthe through holes 3) are opposite to each other, and the other surfaceof the wiring board sheet 1 b (the surface where the conductive paste 8does not protrude from the through holes 3) and the surface of the sheet13 a with a circuit on one side, on which the conductor circuit 5 hasnot been formed, are opposite to each other, and then, these sheets arelayered. At this time, on the respective surfaces that are opposite toeach other, predetermined portions of the conductor circuits 5 arepositioned so as to be placed on the positions of the openings of thethrough holes 3.

Heating and pressing molding is carried out in this condition, andthereby, the wiring board sheet 1 d, the wiring board sheet 1 b, and thesheet 13 a with a circuit on one side, are collectively layered andintegrated.

In this molding process, the resin layer 4 in the B-stage is cured afterbeing melted, and thereby, the interfaces between the wiring board sheet1 d and the wiring board sheet 1 b, and between the wiring board sheet 1b and the sheet 13 a with a circuit on one side, are joined so thatthese sheets are layered and integrated where the insulation layers 16are formed of the cured resin layers 4. In addition, the conductivelayers are formed of the cured conductive paste 8 in the through holes 3filled with the conductive paste 8, and thereby, via holes 15 forelectrically connecting the conductor circuits 5 are formed. At thistime, the conductive paste 8 that has filled the through holes 3 of thewiring board sheet 1 b, has connected the conductor circuits 5 inadvance, as described above, and the conductive paste 8 is cured in thiscondition so as to form the conductive layers, and thus, via holes 15are formed. Furthermore, in the interface between the wiring board sheet1 d and the wiring board sheet 1 b, predetermined portions of theconductor circuit 5 of the wiring board sheet 1 b are connected to theconductive paste 8 that has filled the through holes 3 of the wiringboard sheet 1 d at the time of the above described integration, andthereby, this conductive paste 8 connects the conductor circuits 5, andthe conductive paste 8 is cured in this condition so as to form theconductive layers, and thus, the via holes 15 are formed. Additionally,in the interface between the wiring board sheet 1 b and the sheet 13 awith a circuit on one side, predetermined portions of the conductorcircuit 5 of the wiring board sheet 1 b are connected to the conductivepaste 8 that has filled the through holes 3 of the sheet 13 a with acircuit on one side at the time of the above described integration, andthereby, this conductive paste 8 connects the conductor circuits 5 andthe conductive paste 8 is cured in this condition so as to form theconductive layers, and thus, the via holes 15 are formed.

In addition, at this time, the through holes 3 of the sheet 13 a with acircuit on one side has been filled with the conductive paste 8 in acondensed manner, in advance, as described above, and therefore, the viaholes 15, having a high conductivity and highly reliable connections,are formed. Furthermore, the conductive paste 8 protrudes from theopenings of the through holes 3 of the wiring board sheets 1 b and 1 d,and these protruding portions of the conductive paste 8 are pressed intothe through holes 3 by applying pressure at the time of the abovedescribed collective integration so as to be compressed, and thereby,the via holes 15, having a high conductivity and highly reliableconnections, are formed.

This heating and pressing molding is carried out in a condition wherethe curing response of the resin layer 4 in the B-stage and theconductive paste 8 progresses, and this condition can be set at the samelevel as in the above described cases.

In the multilayer board 11, gained in the above described manner, asshown in FIG. 25( b), the conductor circuits 5 are placed on theoutermost layers on both sides of the multilayer board, respectively,and a two-layered conductor circuit 5 is placed inside the multilayerboard where the via holes 15 for electrically connecting the respectivelayers are formed. In addition, the electric components 10 are placedinside the two layers from among the three insulation layers 16.

In an example shown in FIGS. 26( a) and 26(b), one wiring-board sheet 1f gained in accordance with the process shown in FIGS. 7( a) and 7(b)and two sheets 13 a with a circuit on one side gained in accordance withthe process shown in FIG. 16 are layered and integrated.

In the example shown in FIGS. 26( a) and 26(b), first, a condition isachieved where the surface of one of the sheets 13 a with a circuit onone side on which the conductor circuit 5 has not been formed and asurface of the wiring board sheet 1 f (the surface on which theconductor circuit 5 on which the electric components 10 have not beenmounted has been formed) are opposite to each other and the othersurface of sheet 1 f with a circuit on one side (the surface on whichthe conductor circuit 5 on which the electric components 10 have beenmounted has been formed), and the surface of the sheet 13 a with acircuit on one side on which the conductor circuit 5 has not been formedare opposite to each other, and then, these sheets are layered. At thistime, on the respective surfaces that are opposite to each other,predetermined portions of the conductor circuits 5 are positioned so asto be placed on the positions of the openings of the through holes 3.

Heating and pressing molding is carried out in this condition, andthereby, the two sheets 13 a with a circuit on one side and the onewiring board sheet 1 f are collectively layered and integrated.

In this molding process, the resin layer 4 in the B-stage is cured afterbeing melted, and thereby, the interfaces between one of the sheets 13 awith a circuit on one side and the wiring board sheet 1 f, and betweenthe wiring board sheet 1 f and the other sheet 13 a with a circuit onone side are joined so that the sheets are layered and integrated wherethe insulation layers 16 are formed of the cured resin layers 4. Inaddition, the conductive paste 8 is cured so as to form the conductivelayers in the through holes 3 filled with the conductive paste 8, andthereby, via holes 15 for electrically connecting the conductor circuits5 are formed. At this time, the conductive paste 8 that has filled thethrough holes 3 of the wiring board sheet 1 f has electrically connectedthe conductor circuits 5 in advance as described above, and theconductive paste 8 is cured in this condition so as to form theconductive layers, and thus, the via holes 15 are formed. In addition,in the interfaces between the respective sheets 13 a with a circuit onone side and the wiring board sheet 1 f, predetermined portions of theconductor circuit 5 of the wiring board sheet 1 f are connected with theconductive paste 8 that has filled the through holes 3 of the respectivesheets 13 a with a circuit on one side at the time of the abovedescribed integration, and thereby, this conductive paste connects theconductor circuits 5 and the conductive paste 8 is cured in thiscondition so as to form the conductive layers, and thus, the via holes15 are formed.

In addition, at this time, the through holes 3 of the wiring board sheet1 f and the respective sheets 13 a with a circuit on one side have beenfilled with the conductive paste 8 that is compressed in advance asdescribed above, and therefore, the via holes 15 having a highconductivity and high reliable connections are formed.

This heating and pressing molding is carried out in a condition wherethe curing response of the resin layer 4 in the B-stage and of theconductive paste 8 progresses, and this condition can be set at the samelevel as in the above described cases.

In the multilayer board 11 gained in the above described manner, asshown in FIG. 26( b), the conductor circuits 5 are placed on theoutermost layers on both sides respectively, and a two layered conductorcircuit 5 is placed inside the multilayer board, and in addition, thevia holes 15 for electrically connecting the respective layers areformed. Furthermore, the electric components 10 are placed inside onelayer from among the three insulation layers 16.

In the case where the multilayer board is manufactured as describedabove, the surfaces of the multilayer board become flat and componentsin sheet form made of the resin layer 4 in the B-stage are layered sothat no deformation of the insulation layers 16 occurs in the portionswhere the conductor circuits 5 have been formed in the molding processin a manner where the insulation layers 16 have highly reliableinsulation. Furthermore, the two or more components in sheet form arecollectively layered and integrated, and therefore, it is possible tosimplify the molding process, saving time and effort for a complicatedmolding process, and no difference occurs in the thermal histories ofthe conductor circuits 5 in the respective layers at the time ofmolding, making the correction based on the contraction ratios of theconductor circuits 5 due to the difference in the thermal historiesunnecessary.

In addition, the conductor circuits 5 can be formed in arbitraryportions of the insulation layers 16 in which the via holes 15 have beenformed so that there is more freedom in the wiring design and avia-on-via structure and a pad-on-via structure can be easily formed,making the miniaturization of the circuits and an increase in thedensity easy, and thereby, miniaturization and reduction in thethickness of the wiring board can be achieved and the signal paths canbe shortened.

In addition, the wiring board sheet 1 where conductor circuits have beenformed on both sides, the sheets 13 and the metal foils 9 are used sothat at least one sheet 13 is layered on both sides of the wiring boardsheet 1 and the metal foils 9 are placed on the outermost layers, andafter the sheets and foils have been layered and integrated, throughholes are created so as to penetrate the layered body after being cured,and then, hole plating 18 is formed inside the through holes andsubsequently an etching treatment is carried out on the surfaces of themetal foils 9 on the outermost layers so that the conductor circuits 5are formed, and thereby, the multilayer board 11 can be manufactured.FIGS. 27( a) to 27(c) show one such example.

In an example shown in FIGS. 27( a) to 27(b), one wiring board sheet 1 agained in accordance with the process shown in FIGS. 1( a) to 1(c), twosheets 13 f gained in accordance with the process shown in FIGS. 15( a)to 15(d), and two metal foils 9 are used and these sheets and foils arelayered and integrated.

An appropriate metal foil such as a copper foil is used for the metalfoil 9 and, for example, the same metal foil as in the case where thewiring board sheet 1 e shown in FIG. 6 is manufactured can be used.

In the example shown in FIGS. 27( a) to 27(b), first, the sheets 13 fare placed on both sides of the wiring board sheet 1 a so that thesurfaces of the wiring board sheet 1 a on which the conductor circuits 5have been formed, and one surface of each of the sheets 13 f (thesurfaces where the conductor paste 8 protrudes from the through holes 3)are opposite to each other and the metal foils 9 are placed on the outersides of the respective sheets 13 f so that the other surface of each ofthe sheets 13 f (the surfaces where the conductor paste 8 does notprotrude from the through holes 3) and the rough surfaces of the metalfoils 9 are opposite to each other, and then, these sheets and foils arelayered. At this time, on the respective surfaces of the wiring boardsheet 1 a and of the sheets 13 f that are opposite to each other,predetermined portions of the conductor circuits 5 are positioned so asto be placed on the positions of the openings of the through holes 3.

Heating and pressing molding is carried out in this condition, andthereby, the wiring board sheet 1 a, the sheets 13 f and the metal foils9 are collectively layered and integrated.

In this molding process, the resin layer 4 in the B-stage is cured afterbeing melted, and thereby, the interfaces between the wiring board sheet1 a and the sheets 13 f, and between the sheets 13 f and the metal foils9 are joined so as to be layered and integrated where the insulationlayers 16 are formed of the cured resin layers 4. In addition, theconductive paste 8 is cured so as to form the conductive layers in thethrough holes 3 filled with the conductive paste 8, and thereby, the viaholes 15 for electrically connecting the conductor circuits 5 areformed. In addition, in the interfaces between the wiring board sheet 1a and the sheets 13 f, predetermined portions of the conductor circuits5 of the wiring board sheet 1 a are connected to the conductive paste 8that has filled the through holes three of the sheets 13 f at the timeof the above described integration, while in the interfaces between thesheets 13 f and the metal foils 9, the metal foils 9 are connected tothe conductive paste 8 that has filled the through holes three of thesheets 13 f, and thereby, the conductive circuits 5 and the metal foilsare connected to each other, and the conductive paste 8 is cured in thiscondition so as to form the conductive layers, and thus, the via holes15 are formed.

This heating and pressing molding is carried out in a condition wherethe curing response of the resin layer 4 in the B-stage and of theconductive paste 8 progresses, and this condition can be set at the samelevel as in the above described cases.

Subsequently, through holes 19 are created in predetermined portions ofthe gained layered body so as to penetrate the layered body in thedirection of layering by means of laser processing. These through holes19 are created so as to penetrate the respective resin layers 4(insulation layers 16) and the metal foils 9, and are created so as topenetrate predetermined portions of the conductor circuits 5 in theinner layers (conductor circuits 5 that have been transcribed to thewiring board sheet 1 a) if necessary.

Next, an electroless plating treatment is carried out on the innersurfaces of the created through holes 19 and electrolytic platingtreatment is carried out, if necessary, so that hole plating 18 such ascopper plating is formed, and after that, an etching treatment iscarried out on the metal foils 9 on the outermost layers so as to formthe conductor circuits 5 on the outermost layers (FIG. 27( c)).

In the multilayer board 11 gained in this manner, as shown in FIG. 27(c), the conductor circuits 5 are placed on the outermost layers on bothsides of the multilayer board by carrying out an etching treatment onthe respective metal foils 9, and the two layered conductor circuit 5has been formed inside the multilayer board through transcription fromthe bases 6 for transcription where the via holes 15 for electricallyconnecting the respective layers are formed. In addition, the electriccomponents 10 are placed inside one layer from among the threeinsulation layers 16.

In the case where the multilayer board is manufactured as describedabove, the surfaces of the multilayer board become flat and componentsin sheet form made of the resin layer 4 in the B-stage are layered sothat no deformation of the insulation layers 16 occurs in the portionswhere the conductor circuits 5 have been formed in the molding processin a manner where the insulation layers 16 have highly reliableinsulation. Furthermore, the two or more components in sheet form arecollectively layered and integrated, and therefore, it is possible tosimplify the molding process, saving time and effort for a complicatedmolding process, and no difference occurs in the thermal histories ofthe conductor circuits in the respective layers at the time of molding,making the correction based on the contraction ratios of the conductorcircuits 5 due to the difference in the thermal histories unnecessary.

In addition, the conductor circuits 5 can be formed in arbitraryportions of the insulation layers 16 in which the via holes 15 have beenformed so that there is more freedom in the wiring design and avia-on-via structure and a pad-on-via structure can be easily formed,making the miniaturization of the circuits and an increase in thedensity easy, and thereby, miniaturization and reduction in thethickness of the wiring board can be achieved and the signal paths canbe shortened.

In addition, the conductor circuits 5 on the external layers are formedby carrying out an etching treatment on the metal foils 9 after theinsulation layers 16 have been formed of the cured resin layers 4, andtherefore, the peel strength of the conductor circuits 5 on theseexternal layers is increased, leading to an increase in the landstrength, and as a result, the ability of holding the components mountedon the conductor circuits 5 on these external layers is enhanced.

In addition, additional through holes can be created after theintegration of the layers so as to penetrate the entirety of themultilayer board 11, which makes more freedom in the wiring design.

Such a creation of through holes that penetrate the entirety of themultilayer board 11 after the integration of the layers is not limitedto the present embodiment, but rather such through holes can be createdin any combination of the wiring board sheets 1 and the sheets 13 formanufacturing a multilayer board 11.

In addition, the through holes 19 are created so as to penetrate thelayered body after the integration of the layers so that the holeplating 18 is carried out on the inner surface of the through holes 19,and after that, these through holes 19 are filled in with the conductivepaste 8, and thereby, the through holes can be created so as topenetrate the entirety of the multilayer board 11. In this case, thewiring board sheet 1 where the conductor circuits 5 are formed on bothsurfaces, the sheets 13 having the through holes 3 filled with theconductive paste 8 and the bases 6 for transcription where the conductorcircuits 5 are placed on the surfaces, for example, are used so that atleast 1 sheet 13 is layered on one or two surfaces of the wiring boardsheet 1 and bases 6 for transcription are layered on the external layersof the sheets 13 so that the conductor circuit 5 and the sheets 13 areopposite to each other, and after the sheets and bases have been layeredand integrated, the bases 6 for transcription are released, andsubsequently the protective films 12 are layered on both surfaces of thelayered body. In this condition, the layered body is cured, and afterthat, the through holes 19 are created so as to penetrate the layeredbody where the hole plating 18 is carried out inside the through holes19 and the through holes are filled in with the conductive paste 8, andthen, the protective films 12 are released, and thereby, the multilayerboard 11 can be gained. FIGS. 28( a) to 28(c) show such a example.

In an example shown in FIGS. 28( a) to 28(c) the wiring board sheet 1where the conductor circuits 5 have been formed on both sides (thewiring board sheet 1 a gained in accordance with the process shown inFIGS. 1( a) to 1(c) in the illustrated example), the sheet 13 f gainedin accordance with the process shown in FIGS. 15( a) to 15(b) and thebase 6 for transcription where the conductor circuit 5 has been formedon a surface are used and these sheets and the base are layered andintegrated.

The base 6 for transcription on which the conductor circuit 5 has beenformed which is the same as described above is herein used. At thistime, the base 6 for transcription may be formed of a metal materialsuch as stainless steel, which is the same material as is used in themanufacture of the wiring board sheet 1, or the base 6 for transcriptioncan be formed of a resin film. That is to say, particularly in the casewhere the conductor circuit 5, to be later transcribed, is formed on thebase 6 for transcription and the electric components 10 are mounted atthe time of manufacturing the wiring board sheet 1, the temperature ofthe base 6 for transcription becomes high due to the soldering processat the time of mounting of electric components 10 and sometimes itbecomes necessary to apply a large amount of heat so that the resinlayer 4 is sufficiently melted and softened at the time when theelectric components 10 are buried in the resin layer 4, and therefore, ahigh resistance to heat is required for the base 6 for transcriptionwhile no electric components 10 are mounted on the base 6 fortranscription at the time of the formation of this multilayer board 11where a resistance to heat that is not as high as that at the time ofthe manufacturing of the wiring board sheet 1 is required, and as aresult, the base 6 for transcription can be formed of a resin film. Inthis case, resin films having an adhesive allowing for a release fromthe conductor circuit 5 by means of heating or UV light application suchas, for example, a known PET film and a fluoride based film can be used.

In the illustrated example, first, the sheet 13 f is placed on one ortwo sides (one side in the illustration) of the wiring board sheet 1 aso that the surface of the wiring board sheet 1 a on which the conductorcircuit 5 has been formed and a surface of the sheet 13 f (the surfacewhere the conductive paste 8 protrudes from the through holes 3) areopposite to each other, and the base 6 for transcription on which theconductor circuit 5 has been formed is placed on the outside of thesheet 13 f so that the other surface of the sheet 13 f (the surfacewhere the conductive paste 8 does not protrude from the through holes 3)and the conductor circuit 5 placed on the base 6 for transcription areopposite to each other, and then, these sheets and the base are layered.At this time, on the surfaces of the wiring board sheet and of the sheet13 f that are opposite to each other, predetermined portions of theconductor circuit 5 are positioned so as to be placed on the positionsof the openings of the through holes 3, and on the surfaces of the sheet13 f and of the conductor circuit 9 placed on the base 6 fortranscription that are opposite to each other, predetermined portions ofthe conductor circuit 5 are positioned so as to be placed on thepositions of the openings of the through holes 3.

Heating and pressing molding is carried out in this condition, andthereby, the wiring boarding sheet 1 a, the sheet 13 f and the conductorcircuit 5 that has been placed on the base 6 for transcription arecollectively layered and integrated.

In this molding process, the resin layer 4 in the B-stage is cured afterbeing melted, and thereby, the interfaces between the wiring board sheet1 a and the sheet 13 f, and between the sheet 13 f and the conductorcircuit 5 (placed on the base 6 for transcription) are joined so thatthe sheets and the circuit are layered and integrated where theinsulation layers 16 are formed of the cured resin layers 4. At thistime, the resin layer 4 of the sheet 13 f is melted and softened so asto be fluidized and the conductor circuit 5 that has been placed on thebase 6 for transcription is buried in this resin layer 4.

In addition, the conductive paste 8 is cured so as to form theconductive layers in the through holes 3 filled with the conductivepaste 8, and thereby, the via holes 15 for electrically connecting theconductor circuits 5 are formed. In addition, in the interface betweenthe wiring board sheet 1 a and the sheet 13 f, predetermined portions ofthe conductor circuit 5 of the wiring board sheet 1 a are connected tothe conductive paste 8 that has filled the through holes 3 of the sheet13 f at the time of the above described integration while in theinterface between the sheet 13 f and the conductor circuit 5 (placed onthe base 6 for transcription), predetermined portions of the conductorcircuit 5 are connected to the conductive paste 8 that has filled thethrough holes 3 of the sheet 13 f, and thereby, the conductor circuits 5are connected to each other and the conductive paste 8 is cured in thiscondition so as to form the conductive layers, and thus, the via holes15 are formed. In addition, the portions of the conductive paste 8 thatprotrude from the through holes 3 are pressed into the through holes 3by applying pressure and predetermined portions of the conductor circuit5 are buried in the resin layer 4 in the positions where the throughholes 3 are located, and thereby, the conductive paste 8 is furtherpressed into the through holes 3 so as to be compressed, and thereby,the conductivity of the via holes 15 is increased.

This heating and pressing molding is carried out in a condition wherethe curing response of the resin layer 4 in the B-stage and of theconductive paste 8 progresses, and this condition can be set at the samelevel as in the above described cases.

Subsequently, after the base 6 for transcription has been released fromthe gained layered body, the protective films 12 are layered on bothsides of the layered body and through holes 19 are created in thiscondition by means of laser processing so as to penetrate predeterminedportions of the layered body in the direction of the layering. Thesethrough holes 19 are created so as to penetrate the respective resinlayers 4 (insulation layers 16) and are created if necessary so as topenetrate the conductor circuit 5 that has been transcribed to thewiring board sheet 1 a so as to penetrate predetermined portions of theconductor circuit 5 that has been newly transcribed to the outermostlayers.

Next, an electroless plating treatment is carried out on the innersurfaces of the created through holes 19 and an electrolytic platingtreatment is carried out if necessary so that hole plating 18 suchcopper plating is formed, and after that the conductive paste 8 isapplied to the external surface of the protective films 12 so that thethrough holes 19 are filled in with the conductive paste 8 from theopenings of the through holes 19.

Next, after the protective films 12 have been released from the twosurfaces of the multilayer board, the conductive paste 8 is cured insidethe through holes 19 by applying heat if necessary, and thereby, thethrough holes are created.

In the multilayer board 11 gained in the above described manner as shownin FIG. 28( c), the conductor circuits 5 are buried in the respectiveresin layers 4 (insulation layers 16) on the outermost layers on bothsides so that the conductor circuits 5 are exposed from the surfaces,and the conductor circuit 5 that has been formed through transcriptionby using the base 6 for transcription is placed inside the multilayerboard where the via holes 15 for electrically connecting the respectivelayers are formed. In addition, the electric components 10 are placedinside one of the insulation layers 16.

In the case where the multilayer board is manufactured as describedabove, the surfaces of the multilayer board become flat and componentsin sheet form made of the resin layer 4 in the B-stage are layered sothat no deformation of the insulation layers 16 occurs in the portionswhere the conductor circuits 5 have been formed in the molding processin a manner where the insulation layers 16 have highly reliableinsulation. Furthermore, the two or more components in sheet form arecollectively layered and integrated, and therefore, it is possible tosimplify the molding process, saving time and effort required for acomplicated molding process, and no difference occurs in the thermalhistories of the conductor circuits in the respective layers at the timeof molding, making the correction based on the contraction ratios of theconductor circuits 5 due to the difference in the thermal historiesunnecessary.

In addition, the conductor circuits 5 can be formed in arbitraryportions of the insulation layers 16 in which the via holes 15 have beenformed so that there is more freedom in the wiring design and avia-on-via structure and a pad-on-via structure can be easily formed,making the miniaturization of the circuits and an increase in thedensity easy, and thereby, miniaturization and reduction in thethickness of the wiring board can be achieved and the signal paths canbe shortened.

In addition, additional through holes can be created after theintegration of the layers so as to penetrate the entirety of themultilayer board, which makes more freedom in the wiring design. Inparticular, these through holes secure the conductivity by means of thehole plating 18 and the conductive paste 8, and have highly reliableconductivity.

Such a creation of through holes that penetrate the entirety of themultilayer board 11 after the integration of the layers is not limitedto the present embodiment, but rather in any combination of the wiringboard sheets 1 and the sheets 13 for manufacturing a multilayer board11, through holes 19 are created so as to penetrate the entirety of thelayered body that has been gained by integrating the above describedcombined layers and, after hole plating 18 has been placed on the innersurfaces of the through holes 19, these through holes 19 are filled inwith the conductive paste 8, and thereby, through holes can be createdso as to penetrate the entirety of the multilayer board 11. At thistime, though the through holes penetrating the entirety of themultilayer board 11 have long paths, highly reliable conductivity can besecured by combining the hole plating 18 and the conductive paste 8.

In addition, the embodiment shown in FIGS. 28( a) to 28(c) can bemodified so that the base 6 for transcription on which the conductorcircuit 5 has been placed is not used and the sheet 13 a shown in FIGS.16( a) to 16(c) is used in place of the sheet 13 f. In addition, in thecase where the sheets 13 are layered on the two surfaces of the wiringboard sheet 1, the sheet 13 f and the base 6 for transcription on whichthe conductor circuit 5 has been placed can be layered on one surface ofthe wiring board sheet 1 while the sheet 13 a shown in the FIGS. 16( a)to 16(c) can be layered on the other surface of the wiring board sheet1. FIGS. 29( a) to 29(c) show such an example.

In an example shown in FIGS. 29( a) to 29(c), a wiring board sheet 1,where the conductor circuits 5 have been formed on both sides (thewiring board sheet 1 a gained in accordance with the process shown inFIGS. 1( a) to 1(c) in the illustrated example), a sheet 13 f gained inaccordance with the process, shown in FIGS. 15( a) to 15(d), a sheet 13a gained in accordance with the process, shown if FIGS. 16( a) to 16(c),and a base 6 for transcription, where the conductor circuit 5 has beenformed on a surface, are used, and these sheets and the base are layeredand integrated.

In the example shown in FIGS. 29( a) to 29(c), first, the sheet 13 f isplaced on one surface side of the wiring board sheet 1 a so that thesurface of the wiring board sheet 1 a, on which the conductor circuit 5has been formed, and one surface of the sheet 13 f (the surface wherethe conductive paste 8 protrudes from the through holes 3) are oppositeto each other, and the base 6 for transcription, on which the conductorcircuit 5 has been formed, is placed outside of the sheet 13 f so thatthe other surface of the sheet 13 f (the surface where the conductivepaste 8 does not protrude from the through holes 3) and the conductorcircuit 5 placed on the base 6 for transcription are opposite to eachother, and these sheets and the base are layered. At this time, on thesurfaces of the wiring board sheet 1 a and the sheet 13 f that areopposite to each other, predetermined portions of the conductor circuit5 are positioned so as to be placed on the positions of the openings ofthe through holes 3, and on the surfaces of the sheet 13 f and theconductor circuit 9 that has been placed on the base 6 for transcriptionthat are opposite to each other, predetermined portions of the conductorcircuit 5 are positioned so as to be placed on the positions of theopenings of the through holes 3.

In addition, the sheet 13 a is layered and placed on the other surfaceof the wiring board sheet 1 a so that the surface of the wiring boardsheet 1 a, on which the conductor circuit 5 has been formed, and onesurface of the sheet 13 a (the surface where the conductive paste 8protrudes from the through holes 3) are opposite to each other. At thistime, on the surfaces of the wiring board sheet 1 a and the sheet 13 athat are opposite to each other, predetermined portions of the conductorcircuit 5 are positioned so as to be placed on the positions of theopenings of the through holes 3.

Heating and pressing molding is carried out in this condition so thatthe wiring board sheet 1 a, the sheet 13 a, the sheet 13 f and theconductor circuit 5 that has been placed on the base 6 fortranscription, are collectively layered and integrated.

In this molding process, the resin layers 4 in the B-stage are curedafter being melted, and thereby, the interface between the wiring boardsheet 1 a and the sheet 13 f, the interface between the sheet 13 f andthe conductor circuit 5 (that has been placed on the base 6 fortranscription), and the interface between the wiring board sheet 1 a andthe sheet 13 a, are respectively joined so as to be layered andintegrated where the insulation layers 16 are formed of the cured resinlayers 4. At this time, the resin layer 4 of the sheet 13 f is meltedand softened so as to be fluidized so that the conductor circuit 5 thathas been placed on the base 6 for transcription is buried in this resinlayer 4.

In addition, the conductive paste 8 is cured so as to form theconductive layers in the through holes 3 filled with the conductivepaste 8, and thereby, the via holes 15 for electrically connecting theconductor circuits 5 are formed. In addition, in the interface betweenthe wiring board sheet 1 a and the sheet 13 f, as well as in theinterface between the wiring board sheet 1 a and the sheet 13 a,predetermined portions of the conductor circuit 5 of the wiring boardsheet 1 a are connected to the conductive paste 8 that has filled thethrough holes 3 of the sheets 13 f and 13 a at the time of the abovedescribed integration, and in the interface between the sheet 13 f andthe conductor circuit 5 (that has been placed on the base 6 fortranscription), predetermined portions of the conductor circuit 5 areconnected to the conductive paste 8 that has filled the through holes 3of the sheet 13 f, so that the conductor circuits 5 are connected toeach other, and the conductive paste 8 is cured in this condition so asto form the conductive layers, and thus, the via holes 15 are formed. Inaddition, the portions of the conductive paste 8 that protrude from thethrough holes 3 are pressed into the through holes 3 by applyingpressure, and particularly, in the interface between the wiring boardsheet 1 a and the sheet 13 f, predetermined portions of the conductorcircuit 5 are buried in the resin layer 4 in the positions where thethrough holes 3 are located, and thereby, the predetermined portions arefurther pressed into the through holes 3 so as to be compressed so thatthe conductivity of the via holes 15 is enhanced.

This heating and pressing molding is carried out in a condition wherethe curing response of the resin layer 4 in the B-stage and theconductive paste 8 progresses, and this condition is set at the samelevel as in the above described cases.

Subsequently, after the base 6 for transcription has been released fromthe gained layered body, the protective films 12 are layered and placedon both sides of the layered body, and through holes 19 are created bymeans of laser processing in predetermined portions so as to penetratethe layered body in this condition in the direction of the layering.These through holes 19 are created so as to penetrate the respectiveresin layers 4 (the insulation layers 16) and are created, if necessary,so as to penetrate predetermined portions of the conductor circuits 5,that have been transcribed to the wiring board sheet 1 a and to thesheet 13 a, and predetermined portions of the conductor circuit 5 thathas been newly transcribed to an external layer.

Next, an electroless plating treatment is carried out on the innersurfaces of the created through holes 19, and an electrolytic platingtreatment is carried out, if necessary, so as to form hole plating 18,such as copper plating, and after that, the conductive paste 8 isapplied to the external surfaces of the protective films 12 so that thethrough holes 19 are filled in with the conductive paste 8 from theopenings of the through holes 19.

Next, after the protective films 12 on both sides have been released,the conductive paste 8 is cured in the through holes 19 by applyingheat, if necessary, so as to complete the through holes.

In the multilayer board 11 gained in this manner, as shown in FIG. 29(c), the conductor circuits 5 are placed on the outermost layers on bothsides so that the conductor circuits 5 are buried in the resin layers 4(the insulation layers 16) respectively, and are exposed from thesurfaces, and the conductor circuit 5, that has been formed throughtranscription, is placed in an inner layer of the multilayer board wherethe via holes 15 for electrically connecting the respective layers areformed. In addition, the electric components 10 are placed inside oneinsulation layer 16.

In addition, a wiring board sheet 1, gained in accordance with theprocess shown in FIGS. 11( a) to 11(c), a sheet 13 f, as shown in FIG.15( c), and the base 6 for transcription, on which the conductor circuit5 has been placed, are used so that at least one sheet 13 f is layeredon one or two surfaces of the wiring board sheet 1, and furthermore, thebase 6 for transcription is layered on an external layer so that thisconductor circuit 5 and the sheet 13 f are opposite to each other, andafter the layers have been integrated, the base 6 for transcription isreleased so that the multilayer board 11 can be gained. At this time,the process can be modified so that the base 6 for transcription, onwhich the conductor circuit 5 has been placed, is not used; the sheet 13a, shown in FIGS. 16( a) to 16(c), is used in place of the sheet 13 f;and the sheet 13 a and the wiring board sheet 1 are layered in a mannerwhere the conductor circuit 5, that has been placed on the sheet 13 a,is placed on the external side of the layered body. In addition, in thecase where the sheets 13 are layered on the two surfaces of the wiringboard sheet 1, the sheet 13 f and the base 6 for transcription, on whichthe conductor circuit 5 has been placed, are layered on one surface ofthe wiring board sheet 1 while the sheet 13 a, shown in FIGS. 16( a) to16(c), is layered on the other surface of the wiring board sheet 1.FIGS. 30( a) and 30(b) show such an example.

In the example shown in FIGS. 30( a) and 30(b), a wiring board sheet 1k, gained in accordance with the process shown in FIGS. 11( a) to 11(c),a sheet 13 f, gained in accordance with the process shown in FIGS. 15(a) to 15(d), a sheet 13 a, gained in accordance with the process shownin FIGS. 16( a) to 16(c), and the base 6 for transcription, where theconductor circuit 5 has been formed on a surface, are used, and thesesheets and the base are layered and integrated. Though in theillustrated example, the wiring board sheet 1 k, where the electriccomponents 10 have been mounted on only one side of the conductorcircuit 5 of the conductor circuits 5 on both sides of the wiring boardsheet, is used, the wiring board sheet, where the electric components 10have been mounted on the conductor circuits 5 on both sides, may, ofcourse, be used.

The base 6 for transcription, on which the conductor circuit 5 has beenformed as described above, is used. At this time, though the base 6 fortranscription may be formed of a metal material such as stainless steel,in the same manner as the base for transcription that is used for themanufacturing of the wiring board sheet 1, the base 6 for transcriptioncan be formed of a resin film. That is to say, particularly in the casewhere the conductor circuit 5, to be later transcribed, is formed on thebase 6 for transcription, and the electric components 10 are mounted atthe time of the manufacturing of the wiring board sheet 1, thetemperature of the base 6 for transcription becomes high due to thesoldering process, or the like, at the time of the mounting of theelectric components 10, and sometimes, a large amount of heat must beapplied to the resin layer 4 in a manner where the resin layer 4 issufficiently melted and softened, so that the electric components 10 areburied in the resin layer 4, and therefore, a high resistance to heat isrequired for the base 6 for transcription while no electric components10 are mounted on the base 6 for transcription at the time of themolding of this multilayer board 11, where resistance to heat is not ashigh as at the time of the manufacturing of the wiring board sheet 1,and as a result, the base 6 for transcription can be formed of a resinfilm. In this case, a resin film having an adhesive that allows for therelease from the conductor circuit 5 due to heat or UV lightapplication, such as, for example, a known PET film or a fluoride basedfilm, can be used.

In the illustrated example, first, the sheet 13 f is placed on onesurface side of the wiring board sheet 1 k so that the surface of thewiring board sheet 1 a, on which the conductor circuit 5 has beenformed, and one surface of the sheet 13 f (the surface where theconductive paste 8 protrudes form the through holes 3) are opposite toeach other, and the base 6 for transcription, on which the conductorcircuit 5 has been formed, is placed on an outer side of the sheet 13 fso that the other surface of the sheet 13 f (the surface where theconductive paste 8 does not protrude from the through holes 3) and theconductor circuit 5 that has been placed on the base 6 fortranscription, are opposed to each other, and then, these sheets and thebase are layered. At this time, on the surfaces of the wiring boardsheet 1 k and the sheet 13 f that are opposite to each other,predetermined portions of the conductor circuit 5 are positioned so asto be placed on the positions of the openings of the through holes 3,and on the surfaces of the sheet 13 and the conductor circuit 9, thathas been placed on the base 6 for transcription, that are opposite toeach other, predetermined portions of the conductor circuit 5 arepositioned so as to be placed on the positions of the openings of thethrough holes 3.

In addition, the sheet 13 a is layered and placed on the other surfaceside of the wiring board sheet 1 k so that the surface of the wiringboard sheet 1 k, on which the conductor circuit 5 has been formed, andone surface of the sheet 13 a (the surface where the conductive paste 8protrudes from the through holes 3) are opposite to each other. At thistime, on the surfaces of the wiring board sheet 1 k and the sheet 13 a,predetermined portions of the conductor circuit 5 are positioned so asto be placed on the positions of the openings of the through holes 3.

Heating and pressing molding is carried out in this condition so thatthe wiring board sheet 1 k, the sheet 13 a, the sheet 13 f, and theconductor circuit 5 that has been placed on the base 6 fortranscription, are collectively layered and integrated.

In this molding process, the resin layer 4 in the B-stage is cured afterbeing melted, and thereby, the interface between the wiring board sheet1 k and the sheet 13 f, the interface between the sheet 13 f and theconductor circuit 5 (placed on the base 6 for transcription) and theinterface between the wiring board sheet 1 k and the sheet 13 a, arerespectively joined so as to be layered and integrated where theinsulation layers 16 are formed of the cured resin layers 4. At thistime, the resin layer 4 of the sheet 13 f is melted and softened so asto be fluidized so that the conductor circuit 5 that has been placed onthe base 6 for transcription is buried in this resin layer 4.

In addition, the conductive paste 8 is cured so as to form theconductive layers in the through holes 3 of the sheets 13 f and 13 afilled with the conductive paste 8, and thereby, the via holes 15 areformed. Furthermore, in the interface between the wiring board sheet 1 kand the sheet 13 f, as well as in the interface between the wiring boardsheet 1 k and the sheet 13 a, predetermined portions of the conductorcircuit 5 of the wiring board sheet 1 k are connected to the conductivepaste 8, that has filled the through holes 3 of the sheets 13 f and 13 aat the time of the above described integration, and in the interfacebetween the sheet 13 f and the conductor circuit 5 (that has been placedon the base 6 for transcription), predetermined portions of theconductor circuit 5 are connected to the conductive paste 8 that hasfilled the through holes 3 of the sheet 13 f, so that the conductorcircuits 5 are connected to each other, and the conductive paste 8 iscured in this condition so as to form the conductive layers, and thus,the via holes 15 are formed. In addition, the portions of thisconductive paste 8 that protrude from the through holes 3 are pressedinto the through holes 3 by applying pressure, and particularly in theinterface between the wiring board sheet 1 a and the sheet 13 f,predetermined portions of the conductor circuit 5 are buried in theresin layer 4 in the positions where the through holes 3 are located,and thereby, the predetermined portions are further pressed so as to becompressed in the through holes 3, and thereby, the conductivity of thevia holes 15 is enhanced.

In addition, the portions of the conductive paste 8 or the resin paste20 that has filled the through holes 3 protruding from the through holes3, where hole plating 18 has been formed on the inner surfaces, arepressed into the through holes 3 by applying pressure so that theportions are further pressed into the through holes 3 so as to becompressed, and are cured, and thereby, the via holes 15 are formed.These via holes 15 electrically connect the conductor circuits 9 on bothsides of the wiring board sheet 1 k by means of the hole plating 18, inthe case where the through holes are filled in with the resin paste 20,and by means of the hole plating 18 and the cured conductive paste 8 inthe case where the through holes are filled in with the conductive paste8.

This heating and pressing molding is carried out in a condition wherethe curing response of the resin layer 4 in the B-stage and theconductive paste 8 (as well as the resin paste 20) progresses and thiscondition can be set at the same level as in the above described cases.

Next, the base 6 for transcription is released from the gained layeredbody, and thereby, the multilayer board 11 is gained.

In the multilayer board 11 gained in this manner, as shown in FIG. 30(b), the conductor circuits 5 are placed on the outermost layers on bothsides of the multilayer board so that the conductor circuits 5 arerespectively buried in the resin layers 4 (the insulation layers 16) andare exposed from the surfaces, and the conductor circuit 5, that hasbeen formed through transcription from the base 6 for transcription, isplaced in an inner layer of the multilayer board where the via holes 15for electrically connecting the respective layers are formed. Inaddition, the electric components 10 are placed inside one insulationlayer 16. Furthermore, the conduction of the via holes 15 are secured bythe hole plating 18, exhibiting excellent conduction stability,particularly in the insulation layers 16 where the electric components10 have been buried.

In the case where a multilayer board 11 is fabricated as describedabove, the surfaces are flat and components in sheet form made of theresin layers 4 in the B-stage are layered, and therefore, no deformationof the insulation layers 16 occurs in the portions where the conductorcircuits 5 have been formed in the molding process exhibiting highlyreliable insulation in the insulation layers 16. Furthermore, two ormore components in sheet form are collectively layered and integrated,and therefore, it is possible to simplify the molding process, savingtime and effort required for a complicated molding process, and nodifferences are made in the thermal histories of the conductor circuits5 in the respective layers at the time of molding, making thecorrection, based on the contraction ratio of the conductor circuits 5due to the difference in the thermal histories, unnecessary.

In addition, the conductor circuits 5 can be formed on arbitraryportions of the insulation layers 16 where the via holes 15 are formed,increasing freedom in the wiring design, and a via-on-via structure anda pad-on-via structure can be easily formed making miniaturization ofthe circuits, and an increase in the density, easy to be carried out, sothat scale-down and reduction in the thickness of the wiring board canbe achieved, and the signal paths can be shortened.

In addition, in the embodiment shown in FIGS. 30( a) and 30(b) a wiringboard sheet where the through holes 3 having hole plating 18 are filledin with the resin paste 20 is used as the wiring board sheet 1 k, andsheets such as the sheets 13 f and 13 a that are layered on this wiringboard sheet 1 k where hole plating is not formed inside the throughholes 3, so that the conductivity is secured only by the conductivepaste 8, can be used as the sheets 13 having the through holes 3 filledwith the conductive paste 8. In this case, in the gained multilayerboard 11, the thickness of the insulation layers 16 is increased by thethickness of the electric components 10 when the electric components 10are buried in the resin layers 4 (the insulation layers 16), resultingin an increase in the length of the paths of the via holes 15. However,the conductivity of these via holes 15 is secured by the hole plating18, and thereby, reliable conductivity of the via holes 15 can besecured. At this time, it is preferable to form the hole plating 18 asthick films by carrying out an electrolytic plating treatment followedby an electroless plating treatment. In addition, the insulation layers16 where the electric components 10 are not buried in the resin layers 4(the insulation layers 16) can be formed as thin films so that the pathsof the via holes 15 can be shortened, and therefore, the reliableconductivity of the via holes 15 can be secured only by means of theconductive paste.

In addition, a wiring board sheet 1 gained in accordance with theprocess shown in FIGS. 11( a) to 11(c), a sheet 13 f, as shown in FIG.15( c), and a metal foil 9 such as a copper foil are used so that atleast one sheet 13 f is layered on one or two sides of the wiring boardsheet 1 and the metal foil 9 is layered on the external layer, and afterthe sheets and the foil have been layered and integrated the base 6 fortranscription is released, and thereby, the multilayer board 11 can begained. At this time, the multilayer board 11 can be modified so thatthe metal foil 9 is not used and the sheet 13 c shown in FIG. 18( b) isused in place of the sheet 13 f in a manner where the sheet 13 c and thewiring board sheet 1 are layered where the metal foil 9 of the sheet 13c is placed outside. In addition, in the case where the sheets 13 arelayered on both sides of the wiring board sheet 1, the sheet 13 f andthe metal foils 9 are layered on one surface of the wiring board sheet1, while the sheet 13 c shown in FIG. 18( b) can be layered on the othersurface of the wiring board sheet 1. FIGS. 31( a) to 31(c) show such anexample.

In the example shown in FIGS. 31( a) to 31(c), a wiring board sheet 1 kgained in accordance with the process shown in FIG. 11, a sheet 13 fgained in accordance with the process shown in FIGS. 15( a) to 15(d), asheet 13 c gained in accordance with the process shown in FIGS. 18( a)and 18(b) and a metal foil 9 are used, and these sheets and the foil arelayered and integrated.

An appropriate metal foil such as a copper foil is used as the metalfoil 9 and the same metal foil as in the case where the wiring boardsheet 1 e shown in FIGS. 6( a) and 6(b) is manufactured, for example,can be used.

Though in the illustrated example a wiring board sheet where theelectric components 10 have been mounted on the conductor circuits 5 onboth sides is used as the wiring board sheet 1 k, a wiring board sheetwhere the electric components 10 are mounted only on the conductorcircuit 5 on one side of the wiring board sheet may of course be used.

In the illustrated example, first, the sheet 13 f is layered on onesurface side of the wiring board sheet 1 k so that the surface of thewiring board sheet 1 a on which the conductor circuit 5 has been formedand one surface of the sheet 13 f (the surface where the conductivepaste 8 protrudes from the through holes 3) are opposite to each other,and the metal foil 9 is placed on the outside of the sheet 13 f so thatthe other surface of the sheet 13 f (the surface where the conductivepaste 8 does not protrude from the through holes 3) and one surface(rough surface) of the metal foil 9 are opposite to each other, andthen, these sheets and the foil are layered. At this time, on thesurfaces of the wiring board sheet 1 k and the sheet 13 f that areopposite to each other, predetermined portions of the conductor circuit5 are positioned so as to be placed on the positions of the openings ofthe through holes 3.

In addition, the sheet 13 c is layered and placed on the other surfaceside of the wiring board sheet 1 k so that the surface on which theconductor circuit 5 of the wiring board sheet 1 k has been formed andone surface of the sheet 13 c (the surface on which the metal foil 9 isnot placed) are opposite to each other. At this time, on the surfaces ofthe wiring board sheet 1 k and the sheet 13 c, predetermined portions ofthe conductor circuit 5 are positioned so as to be placed on thepositions of the openings of the through holes 3.

Heating and pressing molding is carried out in this condition so thatthe wiring board sheet 1 k, the sheet 13 c, the sheet 13 f and the metalfoil 9 are collectively layered and integrated.

In this molding process, the resin layers 4 in the B-stage are curedafter being melted, and thereby, the interface between the wiring boardsheet and the sheet 13 f, the interface between the sheet 13 f and themetal foil 9 and the interface between the wiring board sheet 1 k andthe sheet 13 c are respectively joined so as to be layered andintegrated where the insulation layers 16 are formed of the cured resinlayers 4.

In addition, the conductive paste 8 is cured so as to form theconductive layers in the through holes 3 of the sheets 13 f and 13 cfilled with the conductive paste 8, and thereby, the via holes 15 areformed. In addition, in the interface between the wiring board sheet 1 kand the sheet 13 f as well as in the interface between the wiring boardsheet 1 k and the sheet 13 c, predetermined portions of the conductorcircuit 5 on the wiring board sheet 1 k are connected to the conductivepaste 8 that fills the through holes 3 of the sheets 13 f and 13 a atthe time of the above described integration, and in the interfacebetween the sheet 13 f and the metal foil 9, the metal foil 9 isconnected to the conductive paste 8 that has filled the through holes 3of the sheet 13 f, and thereby, the conductor circuit 5 and the metalfoil 9 are connected so that the conductive paste 8 is cured in thiscondition so as to form the conductive layers, and thus, the via holes15 are formed. In addition, the portions of this conductive paste 8formed on the sheet 13 f that protrude from the through holes 3 arepressed into the through holes 3 by applying pressure so as to becompressed in the through holes 3, and thereby, the conductivity of thevia holes 15 is increased.

In addition, the portions of the conductive paste 8 or the resin paste20 that has filled the through holes 3 protruding from the through holes3 of the wiring board sheet 1 k where hole plating 18 is formed on theinner surfaces of the through holes are pressed into the through holesby applying pressure so as to be compressed in the through holes 3 andare cured so as to form the via holes 15. These via holes electricallyconnect the conductor circuits 9 on both sides of the wiring board sheet1 k by means of the hole plating 18 in the case where the through holesare filled in with the resin paste 20 or by means of the hole plating 18and the cured conductive paste 8 in the case where the through holes arefilled in with the conductive paste 8.

This heating and pressing molding is carried out in a condition wherethe curing response of the resin layer 4 in the B-stage and theconductive paste 8 (as well as the resin paste 20) progresses and thiscondition can be set at the same level as in the above described cases.

Subsequently, an etching treatment is carried out on the metal foil 9placed on the outer layer of the gained layered body, and thereby, theconductor circuit 5 is formed on the outermost layer and the multilayerboard 11 is gained.

In the multilayer board 11 gained in this manner, as shown in FIG. 31(c), the conductor circuits 5 are formed by carrying out an etchingtreatment on the respective metal foils 9 on the outer most layers onboth sides of the multilayer board and the conductor circuit 5 formedthrough transcription to the base 6 for transcription is placed in aninner layer of the multilayer board where the via holes 15 forelectrically connecting the respective layers are formed. In addition,the electric components 10 are placed inside one insulation layer 16.Furthermore, particularly in the insulation layer 16 where the electriccomponents 10 have been buried, the conductivity of the via holes 15 issecured by the hole plating 18 exhibiting a high conduction stability.

In the case wherein the multilayer board 11 is fabricated as describedabove, the surfaces are flat and components in sheet form made of theresin layers 4 in the B-stage are layered, and therefore, deformation ofthe insulation layers 16 in the portions where the conductor circuits 5have been formed in the molding process does not occur, and themultilayer board exhibits highly reliable insulation in the insulationlayers 16. Furthermore, the two or more components in sheet form arecollectively layered and integrated, and therefore, it is possible tosimplify the molding process, saving time and effort required for acomplicated molding process, and no differences are made in the thermalhistories of the conductor circuits 5 in the respective layers at thetime of molding, making the correction based on the contraction ratiosof the conductor circuits 5 due to the difference in the thermalhistories unnecessary.

In addition, the conductor circuits 5 can be formed on arbitraryportions of the insulation layers 16 where the via holes 15 have beenformed so that there is more freedom in the wiring design and avia-on-via structure and a pad-on-via structure can be easily formed,and thereby, the miniaturization of the circuits and an increase in thedensity are made easy to be carried out so that the scale-down andreduction in the thickness of the wiring board can be achieved, and thesignal paths can be shortened.

In addition, the conductor circuit 5 on the external layer is formed bycarrying out an etching treatment on the metal foil 9 after theinsulation layer 16 has been formed of the cured resin layer 4, andthereby, the peel strength of the conductor circuit on this externallayer is increased, leading to an increase in the land strength, and theability of holding the components mounted on the conductor circuit 5 onthis external layer is increased.

In addition, in the embodiment shown in FIGS. 31( a) to 31(c), a wiringboard sheet where the through holes 3 having the hole plating 18 arefilled in with the resin paste 20 is used as the wiring board sheet 1 k,particularly in the same manner as in the case shown in FIGS. 30( a) and30(b), while a sheet, such as sheets 13 f and 13 c layered on thiswiring board sheet 1 k, where the hole plating 18 is not formed in thethrough holes 3 so that the conductivity is secured only by theconductive paste 8, can be used as the sheet 13 which has through holes3 filled with the conductive paste 8. In this case, in the gainedmultilayer board 11, the thickness of the insulation layer 16 isincreased by the thickness of the electric components 10 so that thepaths of the via holes 15 are elongated when the electric components 10are buried in the resin layer 4 (the insulation layer 16), and theconductivity of these via holes 15 is secured by the hole plating 18,and thereby, the reliable conductivity of the via holes 15 can besecured. At this time, it is preferable for the hole plating 18 to beformed as a thick film by carrying out an electrolytic plating treatmentfollowed by an electroless plating treatment. In addition, theinsulation layer 16 can be formed as a thin film so that the paths ofthe via holes 15 can be shortened in the resin layer 4 (the insulationlayer 16) in which the electric components 10 are not buried, andtherefore, the reliable conductivity of the via holes 15 can be securedonly by means of the conductive paste 8.

In addition, in the embodiment shown in FIGS. 32( a) to 32(c), a wiringboard sheet 1 h (or 1 i) gained in accordance with the process shown inFIGS. 8( a) to 8(c) or in accordance with the process shown in FIGS. 9(a) to 9(c), a sheet 13 f gained in accordance with the process shown inFIGS. 15( a) to 15(d) and a metal foil 9 are used so that at least onesheet 13 is layered on the surface of the wiring board sheet 1 h (or 1i) on which the conductor circuit 5 has been formed, and furthermore,the metal foil 9 is layered on the external layer, and after the sheetsand the foil have been layered and integrated, through holes are createdso as to penetrate the layered body where hole plating 18 is placed onthe inner surfaces of the through holes and conductor circuits 5 areformed by carrying out an etching treatment on the metal foils on thetwo external layers, and thus, the multilayer board 11 is gained.

An appropriate metal foil, such as a copper foil, is used as the metalfoil 9 and the same metal foil as in the case where the wiring boardsheet 1 e shown in FIGS. 6( a) and 6(b) is manufactured, for example,can be used.

In the illustrated example, first, the sheet 13 f is placed on one sideof the wiring board sheet 1 h (or 1 i) on which the conductor circuit 5has been formed so that the surface of the wiring board sheet 1 h (or 1i) on which the conductor circuit 5 has been formed and one surface ofthe sheet 13 f (the surface where the conductive paste 8 protrudes fromthe through holes 3) are opposite to each other, and the metal foil 9 isplaced on the outside of the sheet 13 f so that the other surface of thesheet 13 f (the surface where the conductive paste does not protrudefrom the through holes 3), and one surface (rough surface) of the metalfoil 9 are opposite to each other and these sheets and the foil arelayered. At this time, on the surfaces of the wiring board sheet 1 h (or1 i) and the sheet 13 f that are opposite to each other, predeterminedportions of the conductor circuit 5 are positioned so as to be placed onthe positions of the openings of the through holes 3.

Heating and pressing molding is carried out in this condition, andthereby, the wiring board sheet 1 h (or 1 i), the sheet 13 f and themetal foil 9 are collectively layered and integrated.

In this molding process, the resin layers 4 in the B-stage are curedafter being melted, and thereby, the interface between the wiring boardsheet 1 h (or 1 i) and the sheet 13 f as well as the interface betweenthe sheet 13 f and the metal foil 9 are joined respectively so as to belayered and integrated where the insulation layers 16 are formed of thecured resin layers 4.

In addition, the conductive paste 8 is cured so as to form theconductive layers in the through holes of the sheet 13 f filled with theconductive paste 8, and thereby, the via holes 15 are formed. Inaddition, in the interface between the wiring board sheet 1 h (or 1 i)and the sheet 13 f, predetermined portions of the conductor circuit 5 onthe wiring board sheet 1 k are connected to the conductive paste 8 thathas filled the through holes 3 of the sheet 13 f at the time of theabove described integration and in the interface between the sheet 13 fand the metal foil 9, the metal foil 9 is connected to the conductivepaste 8 that has filled the through holes 3 of the sheet 13 f so thatthe conductor circuit 5 and the metal foil are connected to each otherand the conductive paste 8 is cured in this condition so as to form theconductive layers, and thus, the via holes 15 are formed. In addition,the portions of this conductive paste 8 protruding from the throughholes 3 that has been formed on the sheet 13 f are pressed into thethrough holes 3 by applying pressure so as to be compressed in thethrough holes, and thereby, the conductivity of the via holes 15 isincreased.

This heating and pressing molding is carried out in a condition wherethe curing response of the resin layer 4 in the B-stage and theconductive paste 8 (as well as the resin paste 20) progresses, and thiscondition can be set at the same level as in the above described cases.

Subsequently, through holes 19 are created by means of laser processingso as to penetrate predetermined portions of the gained layered body inthe direction of the layering. These through holes 19 are created so asto penetrate the resin layers 4 (the insulation layers 16) and the metalfoil 9, and are created, if necessary, so as to penetrate predeterminedportions of the conductor circuit 5 (the conductor circuit 5 that hasbeen transcribed to the wiring board sheet 1 h or 1 i) inside thelayered body.

Next, an electroless plating treatment is carried out on the innersurfaces of the created through holes 19, and an electrolytic platingtreatment is carried out if necessary so that the conductor circuits 5are formed on the outer most layers by carrying out an etching treatmenton the metal foils 9 on the outer most layers after the formation of thehole plating 18 such as copper plating (FIG. 32( c)).

In the multilayer board 11 gained in this manner, as shown in FIG. 31(c), the conductor circuits 5 are formed by carrying out an etchingtreatment on the respective metal foils 9 on the outermost layers onboth sides of the multilayer board, and the conductor circuit 5 formedthrough transcription from the base 6 for transcription is placed insidethe multilayer board where the via holes 15 for electrically connectingthe respective layers are formed. In addition, the electric components10 are placed inside one insulation layer 16.

In the case wherein the multilayer board 11 is fabricated as describedabove, the surfaces are flat and components in sheet form made of theresin layers 4 in the B-stage are layered, and therefore, deformation ofthe insulation layers 16 in the portions where the conductor circuits 5have been formed in the molding process does not occur, and themultilayer board exhibits highly reliable insulation in the insulationlayers 16. Furthermore, the two or more components in sheet form arecollectively layered and integrated, and therefore, it is possible tosimplify the molding process, saving time and effort required for acomplicated molding process, and no differences are made in the thermalhistories of the conductor circuits 5 in the respective layers at thetime of molding, making the correction based on the contraction ratiosof the conductor circuits 5 due to the difference in the thermalhistories unnecessary.

In addition, the conductor circuits 5 can be formed on arbitraryportions of the insulation layers 16 where the via holes 15 have beenformed so that there is more freedom in the wiring design and avia-on-via structure and a pad-on-via structure can be easily formed,and thereby, the miniaturization of the circuits and an increase in thedensity are made easy to be carried out so that the scale-down andreduction in the thickness of the wiring board can be achieved, and thesignal paths can be shortened.

In addition, the conductor circuit 5 on the external layer is formed bycarrying out an etching treatment on the metal foil 9 after theinsulation layer 16 has been formed of the cured resin layer 4, andthereby, the peel strength of the conductor circuit on this externallayer is increased, leading to an increase in the land strength, and theability of holding the components mounted on the conductor circuit 5 onthis external layer is increased.

In addition, additional through holes can be created so as to penetratethe entirety of the multilayer board 11 after the formation of thelayered body so that there is more freedom in the wiring design.

The embodiment shown in FIGS. 33( a) to 33(d) is an example which ismultilayered by means of a build-up manufacturing method. In the casewhere a multilayer is formed in accordance with the build-upmanufacturing method, a variety of wiring board sheets 1, as describedabove, or a multilayer board 11 manufactured by using wiring boardsheets 1 can be used as the core material. In the example shown in FIGS.33( a) to 33(d) a wiring board sheet 1 k gained in accordance with theprocess shown in FIGS. 11( a) to 11(c) is used as the core material.

In the illustrated example, first, as shown in FIG. 33( a), a metal foil17 with resin is layered on one or two sides (two sides in theillustration) of the core material (wiring board sheet 1 k) as the sheet13 having the resin layer 4 so that the metal foil 9 is placed on theouter surface, and then, the sheets and the foils are layered andintegrated by means of heating and processing molding.

At this time, the core material before being integrated may have theresin layer 4 in the B-stage, or the resin layer 4 may be in theC-stage. In addition, the metal foil 17 with resin can be gained byforming the resin layer 4 in the B-stage on one surface of the metalfoil 9 such as copper foil, and for example, a metal foil formed in thesame manner as in the manufacture of the wiring board sheet 1 i shown inFIG. 9 can be used.

In this molding process, the resin layer 4 in the B-stage is cured afterbeing melted, and thereby, the interface between the wiring board sheet1 k, which is the core material, and the sheet 13 (the metal foil 17with resin) is joined so that these sheets are layered and integratedwhere the insulation layers 16 are formed of the cured resin layers 4.

Next, non-through holes 21 are created so as to penetrate only the metalfoil 9 and the resin layer 4 of the lower layer of this metal foil, byirradiating the metal foil 9, which is the outermost layer, with a laserbeam. These non-through holes 21 are created at predetermined positionsof the conductor circuit 5, that has been formed on the wiring boardsheet 1 (1 k) which is the core material, and these non-through holes 21are created so that the surface of the conductor circuit 5 that has beenformed on this wiring board sheet 1 (1 k), is exposed from the bottomsof the non-through holes 21.

Then, hole plating 18 is formed on the inner surfaces of the non-throughholes 21. Copper plating or the like can be carried out as the holeplating 18 which can be formed by carrying out electrolytic plating, ifnecessary, after electroless plating, for example, has been carried out.

Next, an etching process is carried out on the metal foil 9, which isthe external layer, so as to form the conductor circuit 5. At this time,the non-through holes 21, in which the hole plating 18 has been formed,are created as the via holes 15, that electrically connect the conductorcircuits 5.

As a result of this, in the illustrated example, as shown in FIG. 33(b), a multilayer board 11 having a four-layered conductor circuit 5 andthree insulation layers 16 is gained. At this time, the conductionbetween the layers crossing the insulation layers 16, where theelectrical connections 10 have been buried, is secured by the via holes15 made of the through holes 3, where the hole plating 18 has beenformed on the inner surfaces and which are filled with the conductivepaste 8 or resin paste 20 in the multilayer board 11. In addition, theconduction between the layers crossing the insulation layer 16, wherethe electric components 19 have not been buried, is secured by the viaholes 15 made of non-through holes 21, where the hole plating 18 hasbeen formed on the inner surfaces.

Here, these non-through holes 21 where the hole plating 18 has beenformed on the inner surfaces may be further filled with conductive pasteor resin paste which is then cured.

Furthermore, additional layers can be formed on the multilayer board 11that has been formed as described above. In such a case, as shown inFIG. 33( c), for example, a metal foil 17 with resin, which is the samemetal foil as described above, is placed and layered on one or two sides(two sides in the illustration) of the multilayer board 11 as the sheet13, in a manner where the metal foil 9 is placed on the external side,and heating and pressing molding is carried out on the multilayer boardand the sheet so that the multilayer board and the sheet are layered andintegrated.

In this molding process, the resin layer 4 in the B-stage of the metalfoil 17 with resin is cured after being melted, and thereby, theinterface between the multilayer board 11 and the sheet 13 (the metalfoil 17 with resin) is joined, so that the multilayer board and thesheet are layered and integrated where the insulation layers 16 areformed of the cured resin layers 4. In addition, at this time, themelted resin flows into these non-through holes 21 so as to fill thesenon-through holes 21, in the case where the via holes 15, made ofnon-through holes 21 where the hole plating 18 has been formed on theinner layer, have not been filled with conductive paste or resin paste.

Subsequently, in the same manner as in the above described case, themultilayer board 11, to which additional layers have been added, can begained as shown in FIG. 33( d) by creating the non-through holes 21, byforming the hole plating 18 and by forming the conductor circuits 5 onthe external layers.

In addition, such formation of the insulation layer 16 and the conductorcircuit 5 is repeated so that a multilayer board 11, to which additionallayers are further added, can be gained.

The addition of the layers by means of the build-up manufacturingmethod, is not limited to the one as described above, but rather theformation of layers of the insulation layers 16 can be carried out byapplying and curing resin paste, or the formation of layers of theconductor circuits 5 can be carried out by means of a plating treatment.In addition, when the via holes 15 are formed in the insulation layers16 that have been layered on the core material, the via holes 15 can beformed by filling the non-through holes 21 with conductive paste, whichis then cured, without forming the hole plating 18 after the non-throughholes 21 have been created as described above. Furthermore, a variety ofother techniques, which are carried out in accordance with the build-upmanufacturing method, can be adopted.

The multilayer board 11 that is gained in this manner can be formed as amultilayered wiring board that incorporates high level LCR functions,and can be expected to be utilized in a microelectronic field, such as acompact high frequency module including an RF module and a blue toothmodule.

In the following, the embodiments of the present invention are describedin detail.

Embodiment 1

Slurry that contains components shown in Table 1 is kneaded with aplanetary mixer and the viscosity is adjusted to 3000 cP by mixing aproper amount of solvent into the slurry, and thereby, a resincomposition is gained.

This resin composition is applied to a carrier base 7 made of a rolledcopper foil, which is heated and dried for 5 minutes at 140° C., andthereby, a resin sheet 4 a in the B-stage having a thickness of 100 μmis formed on one surface of the carrier base 7.

On the other hand, a soft etching treatment is carried out using aferric chloride solution on the surface of a stainless steel base madeof SUS301 having a thickness of 100 μm, and thereby, a base 6 fortranscription having a surface roughness Ra of 0.3 μm is gained. Aplating resist is formed on the surface of this base 6 for transcriptionand the plating resist is released after an electrolytic copper platingtreatment has been carried out, and then, a conductor circuit 5 isformed to have a thickness of 15 μm. Furthermore, resistors in chip formand capacitors in chip form, which are electric components 10, aresoldered to this conductor circuit 5 by means of a solder reflowtreatment, and thereby, the electric components 10 are mounted on theconductor circuit 5. The solder reflow treatment is carried out byapplying heat at a maximum temperature of 260° C. for 15 seconds.

Subsequently, six resin sheets 4 a, each of which is the same as theabove described resin sheet 4 a, from which the carrier base 7 has beenremoved, are placed and layered on a side of the base 6 fortranscription on which the conductor circuit 5 has been formed, andthen, the base 6 for transcription is released so that the conductorcircuit 5 remains on the resin layer 4 after heating and pressingmolding has been carried out in a vacuum for 10 minutes at a heatingtemperature of 130° C. under an applied pressure of 0.294 MPa.

Subsequently, a protective film 12 having a thickness of 100 μm made ofPET is layered and placed on one surface of the resin layer 4 on theside on which the conductor circuit 5 has not been formed, and theprotective film 12 side is irradiated with a YAG laser in a condition of15 KHz, 1 W and 15 shots, and thereby, a through hole 3 having an innerdiameter of 300 μm is created so as to penetrate the resin layer 4, theprotective film 12, and the conductor circuit 5 on one surface of theresin layer 4.

Next, conductive paste 8 (made by Tatsuta Electric Wire & Cable Co.,Ltd., model number “AE1244”) is applied to the external surface of theprotective film 12 using a spatula so that the through holes 3 arefilled in with this conductive paste 8, and after that, the protectivefilm 12 is released from the resin layer 4. Thus, two wiring boardsheets 1 d are gained.

In addition, the base 6 for transcription, on which the conductorcircuit 5 has been formed, is layered and placed on the surface of resinlayer 4, on the side where the conductor circuit 5 has not been formed,of a wiring board sheet that has been formed in the same manner as theabove described wiring board sheets 1 d, so that the surface on whichthe conductor circuit 5 has been formed is opposite to the resin layer4, in a condition where the through holes 3 and the conductor circuit 5are in alignment. The base 6 for transcription, on which the conductorcircuit 5 has been formed, has been formed in the same manner as in thecase of the above described wiring board sheets 1 d.

In this condition, heating and pressing molding is carried out in avacuum for 10 minutes at a heating temperature of 130° C. under anapplied pressure of 0.490 MPa, and after that, the base 6 fortranscription is released so that the conductor circuit 5 remains on theresin layer 4, and thereby, a wiring board sheet if is gained.

Then, the above described wiring board sheets 1 d and 1 f are layered inthe same manner as shown in FIG. 24( a) and 24(b), and heating andpressing molding is carried out in a vacuum for 90 minutes at a heatingtemperature of 175° C. and an applied pressure of 2.94 MPa so that thesheets are layered and integrated, and thus, a multilayer board 11 isgained.

Embodiment 2

Slurry that contains components shown in Table 1 is kneaded with aplanetary mixer and the viscosity is adjusted to 3000 cP by mixing aproper amount of solvent into the slurry, and thereby, a resincomposition is gained.

This resin composition is applied to a carrier base 7 made of apolyethylene terephthalate film which is heated and dried for 8 minutesat 130° C., and thereby, a resin sheet 4 a in the B-stage having athickness of 100 μm is formed on one surface of the carrier base 7.

On the other hand, a plating resist is formed on a surface of the base 6for transcription in the same manner as in the case of Embodiment 1, andthe plating resist is released after an electrolytic copper platingtreatment has been carried out, and thereby, a conductor circuit 5having a thickness of 15 μm is formed. Furthermore, inductors in chipform and bare silicon chips, which are electric components 10, areconnected to this conductor circuit 5 via solder balls. Heat is appliedat 260° C. for 20 seconds at the time when the connections are made bymeans of the solder balls. In addition, after the electric components 10have been mounted, underfill is placed beneath the bare silicon chipsand is pre-dried at 150° C. for 10 minutes.

Subsequently, five resin sheets 4 a, each of which is the same as theabove described resin sheet 4 a, from which the carrier base 7 has beenremoved, are placed and layered on a side of the base 6 fortranscription on which the conductor circuit 5 has been formed, andthen, the base 6 for transcription is released so that the conductorcircuit 5 remains on the resin layer 4 after heating and pressingmolding has been carried out in a vacuum for 10 minutes at a heatingtemperature of 130° C. under an applied pressure of 0.294 MPa.

Subsequently, in the same manner as in the case in Embodiment 1, athrough hole 3, having an internal diameter of 300 μm, is created so asto penetrate the resin layer 4, the protective film 12, and theconductor circuit 5 on one side of the resin layer 4.

Next, conductive paste 8 (made by Tatsuta Electric Wire & Cable Co.,Ltd., model number “AE1244”) is applied to the external surface of theprotective film 12 using a spatula so that the through holes 3 arefilled in with this conductive paste 8, and after that, the protectivefilm 12 is released from the resin layer 4. Thus, two wiring boardsheets 1 d are gained.

In addition, an electrolytic copper foil having a thickness of 18 μm islayered and placed on the surface of resin layer 4, on the side wherethe conductor circuit 5 has not been formed, of a wiring board sheetthat has been formed in the same manner as the above described wiringboard sheets 1 d, and heating and pressing molding is carried out on thelayers in this condition in a vacuum for 10 minutes at a heatingtemperature of 130° C. under an applied pressure of 0.490 MPa, and thus,a wiring board sheet 1 e is gained.

Then, the above described two wiring board sheets 1 d and one wiringboard sheet 1 e are layered in a condition where the surface of thewiring board sheet 1 e on which the conductor circuit 5 has been formed,and the surface of one of the wiring board sheets 1 d on which theconductor circuit 5 has not been formed, are opposite to each other, andthe surface of the wiring board sheet 1 d on which the conductor circuit5 has been formed, and the surface of the other wiring board sheet 1 don which the conductor circuit 5 has been formed, are opposite to eachother, and then, heating and pressing molding is carried out in a vacuumfor 90 minutes at a heating temperature of 175° C. under an appliedpressure of 2.94 MPa so that the layers are integrated and a multilayerboard 11 is gained.

Embodiment 3

Slurry that contains components shown in Table 1 is kneaded with aplanetary mixer and the viscosity is adjusted to 3000 cP by mixing aproper amount of solvent into the slurry, and thereby, a resincomposition is gained.

This resin composition is applied to a carrier base 7 made of apolyethylene terephthalate film which is heated and dried for 8 minutesat 130° C., and thereby, a resin sheet 4 a in the B-stage having athickness of 100 μm is formed on one surface of the carrier base 7.

On the other hand, a plating resist is formed on a surface of the base 6for transcription in the same manner as in the case of Embodiment 1, andthe plating resist is released after an electrolytic copper platingtreatment has been carried out, and thereby, a conductor circuit 5having a thickness of 12 μm is formed. Furthermore, electric components10 are mounted on this conductor circuit 5 in the same manner as inEmbodiment 1.

Subsequently, eight resin sheets 4 a, each of which is the same as theabove described resin sheet 4 a, from which the carrier base 7 has beenremoved, are placed and layered on a side of the base 6 fortranscription on which the conductor circuit 5 has been formed, andthen, the base 6 for transcription is released so that the conductorcircuit 5 remains on the resin layer 4 after heating and pressingmolding has been carried out in a vacuum for 10 minutes at a heatingtemperature of 130° C. under an applied pressure of 0.294 MPa.

Subsequently, in the same manner as in the case in Embodiment 1, athrough hole 3, having an internal diameter of 300 μm, is created so asto penetrate the resin layer 4, the protective film 12, and theconductor circuit 5 on one side of the resin layer 4.

Next, conductive paste 8 (made by Tatsuta Electric Wire & Cable Co.,Ltd., model number “AE1244”) is applied to the external surface of theprotective film 12 using a spatula so that the through holes 3 arefilled in with this conductive paste 8, and after that, the protectivefilm 12 is released from the resin layer 4. Thus, two wiring boardsheets 1 d are gained.

In addition, two bases 6 for transcription that have been gained in thesame manner as described above, are placed so that the surfaces on whichthe conductor circuits 5 have been formed are opposite to each other,and six resin sheets 4 a, each of which is the same resin sheet 4 a asdescribed above from which the carrier base 7 has been removed, areplaced between the two bases 6 for transcription so that these bases andsheets are layered and heating and pressing molding is carried out in avacuum for 10 minutes at a heating temperature of 130° C. under anapplied pressure of 0.294 Mpa, and after that, the bases 6 fortranscription are released so that the conductor circuits 5 remain onthe resin layer 4. Subsequently, a protective film 12 made of PET havinga thickness of 75 μm is layered and placed on one surface of the resinlayer 4, and a through hole 3 having an inner diameter of 300 μm iscreated by means of a laser irradiation under the same conditions as inEmbodiment 1, so as to penetrate the resin layer 4, the protective film12, and the conductor circuits 5 on both sides of the resin layer 4.

Next, conductive paste 8 (made by Tatsuta Electric Wire & Cable Co.,Ltd., model number “AE1244”) is applied to the external surface of theprotective film 12 using a spatula so that the through holes 3 arefilled in with this conductive paste 8, and after that, the protectivefilm 12 is released from the resin layer 4, and thus, a wiring boardsheet 1 b is gained.

In addition, the above described resin composition is applied to acarrier base 7 made of a polyethylene terephthalate film having athickness of 100 μm, which is heated and dried for 9 minutes at 130° C.,and thereby, a resin layer 4 in the B-stage having a thickness of 100 μmis formed on one surface of the carrier base 7.

Subsequently, the carrier base 7 side is irradiated with a carbonic acidgas laser under the conditions of 7.1 mJ, 100 Hz, 1 shot and a pulsewidth of 35 μs, and thereby, a through hole 3 having an inner diameterof 100 μm is created so as to penetrate the carrier base 7 and the resinlayer 4.

Next, conductive paste 8 (made by Tatsuta Electric Wire & Cable Co.,Ltd., model number “AE1244”) is applied to the external surface of theprotective film 12 using a spatula so that the through holes 3 arefilled in with this conductive paste 8, and after that, the carrier base7 is released from the resin layer 4.

Subsequently, the base 6 for transcription on which the conductorcircuit 5 has been formed, and the above described resin layer 4, arelayered so that the conductor circuit 5 and the resin layer 4 areopposite to each other and the through holes 3 and the conductor circuit5 are aligned, and heating and pressing molding is carried out in avacuum for 10 minutes at a heating temperature of 130° C. under anapplied pressure of 2.94 MPa. After that, the base 6 for transcriptionis released so that the conductor circuit 5 remains on the resin layer4, and thereby, a sheet 13 a with a circuit on one side is gained. Thebase 6 for transcription on which the conductor circuit 5 has beenformed, has been formed in the same manner as in the case of the abovedescribed wiring board sheets 1 d.

Then, the above described wiring board sheets 1 d, 1 b and the sheet 13a with a circuit on one side, are layered in the same manner as shown inFIGS. 25( a) and 25(b), and heating and pressing molding is carried outin a vacuum for 90 minutes at a heating temperature of 175° C. under anapplied pressure of 2.94 MPa so that the layers are integrated and amultilayer board 11 is gained.

Embodiment 4

Slurry that contains components shown in Table 1 is kneaded with aplanetary mixer and the viscosity is adjusted to 3000 cP by mixing aproper amount of solvent into the slurry, and thereby, a resincomposition is gained.

This resin composition is applied to a carrier base 7 made of apolyethylene terephthalate film which is heated and dried for 10 minutesat 150° C., and thereby, a resin sheet 4 a in the B-stage having athickness of 100 μm is formed on one surface of the carrier base 7.

On the other hand, a soft etching treatment is carried out using aferric chloride solution on the surface of a stainless steel base madeof SUS304 having a thickness of 100 μm, so that the base 6 fortranscription of which the degree of surface roughness, Ra, is 0.25 μm,is gained. A plating resist is formed on a surface of this base 6 fortranscription and the plating resist is released after an electrolyticcopper plating treatment has been carried out, and thereby, a conductorcircuit 5 having a thickness of 15 μm is formed. Furthermore, capacitorpaste (one-component polymer based dielectric paste which containsbarium titanate powder that has been mixed in a mixed binder of an epoxyresin and a melamine resin, which has been kneaded so that the powder isdispersed is the binder, made by Asahi Chemical Research Laboratory Co.,Ltd., CX-16) and resistor paste (carbon resistor paste that containscarbon powder uniformly dispersed in a phenol resin binder, made byAsahi Chemical Research Laboratory Co., Ltd., TU-100-8), which areelectric components 10, are printed on or applied to this base 6 fortranscription, and are cured by heating and drying for 30 minutes at150° C. and for 60 minutes at 170° C., respectively. In addition, copperpaste (made by Asahi Chemical Research Laboratory Co., Ltd., LS-504J) isapplied to the base and is cured by heating and drying for 30 minutes at150° C., and then, electrodes of capacitor elements are formed.

Subsequently, two bases 6 for transcription are placed so that thesurfaces on which the conductor circuits 5 have been formed are oppositeto each other, and seven resin sheets 4 a, each of which is the same asthe above described resin sheet 4 a from which the carrier base 7 hasbeen removed, are layered between the two bases, and the layers arecured by applying heat for 15 minutes at 175° C. under a pressure of0.294 MPa, and after that, the bases 6 for transcription are released sothat the conductor circuits 5 remain on the resin layer 4.

Subsequently, protective films 12 made of PET having a thickness of 50μm are layered and placed on both sides of the resin layer 4, and one ofthe sides of the protective films 12 is irradiated with a YAG laserunder conditions of 15 KHz, 1.8 W and 50 shots, and thereby, a throughhole 3 having an inner diameter of 300 μm is created so as to penetratethe resin layer 4, the protective films 12, and the conductor circuits 5on both sides of the resin layer 4.

An electroless copper plating treatment is carried out on the innersurface of this through hole 3 so as to form hole plating 18 having athickness of 0.2 μm, and after that, conductive paste 8 (made by TatsutaElectric Wire & Cable Co., Ltd., model number “AE1244”) is applied tothe external surface of the protective film 12 using a spatula so thatthe through hole 3 is filled in with this conductive paste 8, which ispreliminary dried for 60 minutes at 80° C., and after that, theprotective film 12 is released from the resin layer 4. Thus, a wiringboard sheet 1 k is gained.

In addition, the above described resin composition is applied to thecarrier base 7 made of a polyethylene terephthalate film having athickness of 100 μm, which is heated and dried for 9 minutes at 130° C.so that a resin layer 4 in the B-stage having a thickness of 100 μm isformed on one surface of the carrier base 7.

Subsequently, the carrier base 7 side is irradiated with a carbonic acidgas laser under the conditions of 7.1 mJ, 100 Hz, 1 shot and a pulsewidth of 35 μs, and thereby, a through hole 3 having an inner diameterof 100 μm is created so as to penetrate the carrier base 7 and the resinlayer 4.

Next, conductive paste 8 (made by Tatsuta Electric Wire & Cable Co.,Ltd., model number “AE1244”) is applied to the external surface of thecarrier base 7 using a spatula so that the through holes 3 are filled inwith this conductive paste 8, and after that, the carrier base 7 isreleased from the resin layer 4 so that a sheet 13 f having throughholes 3 filled with the conductive paste 8 is gained.

In addition, a plating resist is formed on a surface of a base 6 fortranscription formed of a stainless steel base made of SUS304 having athickness of 100 μm, and the plating resist is released after anelectrolytic copper plating treatment has been carried out so that aconductor circuit 5 having a thickness of 15 μm is formed, and the base6 for transcription on which the conductor circuit 5 has been formed isgained.

Then, sheets 13 f are placed on both sides of the wiring board sheet 1 kso that the surface of the sheets 13 f, from which the conductive paste8 protrudes, are opposite to the wiring board sheet 1 k and bases 6 fortranscription, on which the conductor circuits 5 have been formed, areplaced and layered on the outer layers of the sheets 13 f so that theconductor circuits 5 are opposite to the sheets 13 f, and heating andpressing molding is carried out for 60 minutes at a heating temperatureof 175° C. under an applied pressure of 2.94 MPa so that the layers areintegrated and a multilayer board 11 is gained.

Embodiment 5

Slurry that contains components shown in Table 1 is kneaded with aplanetary mixer and the viscosity is adjusted to 3000 cP by mixing aproper amount of solvent into the slurry, and thereby, a resincomposition is gained.

A glass unwoven cloth (made by Oribest Co., Ltd., SAS series, having aweight of 25 g/cm², and a thickness of 200 μm) is impregnated with thisresin composition, which is dried for 5 minutes at 160° C. so that aresin sheet 4 a having a thickness of 200 μm is fabricated.

On the other hand, a soft etching is carried out using a mixed solutionof nitric acid and hydrofluoric acid on the surface of a stainless steelbase made of SUS304 having a thickness of 100 μm so that a base 6 fortranscription having a degree of surface roughness, Ra, of 0.3 μm isgained. After a pattern of a plating resist has been formed on thesurface of this base 6 for transcription, a copper plating is formed bymeans of an electrolytic copper plating treatment and furthermore,plating treatments are carried out in the order of nickel plating andgold plating, and after that, the resist is released so as to form aconductor circuit 5 having a thickness of 15 μm. Furthermore, ICs (flipchips), resistors in chip form and capacitors in chip form, which areelectric components 10, are soldered to this conductor circuit 5 bymeans of a solder reflow treatment, and thus, the electric components 10are mounted on the conductor circuit 5. The solder reflow treatment iscarried out by applying heat for 15 seconds at a maximum temperature of260° C. In addition, underfill (made by Matsushita Electric Works, Ltd.,CV5183) is placed beneath the ICs and is heated and cured for 30 minutesat 150° C.

In addition, the above described resin composition is applied to therough surface side of a copper foil having a thickness of 18 μm, whichis dried for 10 minutes at 130° C. so that a metal foil 17 with resinthat has a resin layer 4 b having a thickness of 50 μm.

Subsequently, three resin sheets 4 a, each of which is the same as theabove described resin sheet 4 a, are layered on the surface of the base6 for transcription on which the conductor circuit 5 has been formed,and furthermore, the metal foil 17 with resin is layered and placed onthe external surface side of the outer most resin sheet 4 a so that theresin layer 4 b is opposite to the resin sheet 4 a and heating andpressing molding is carried out in a vacuum for 15 minutes at a heatingtemperature of 175° C. under an applied pressure of 0.294 MPa and afterthat, the base 6 for transcription is released so that the conductorcircuit 5 remains on the resin layer 4. Thereby, a wiring board sheet 1i is gained.

In addition, the above described resin composition is applied to acarrier base 7 made of a PET film having a thickness of 100 μm, which isthen heated and dried for 5 minutes at 130° C., and thereby, a resinlayer 4 in the B-stage having a thickness of 100 μm is formed.

Subsequently, a carbonic acid gas laser is emitted under the conditionsof 7.1 mJ, 100 Hz, 1 shot and a pulse width of 35 μs, and thereby,through holes 3 having an inner diameter of 100 μm are created so as topenetrate the carrier base 7 and the resin layer 4.

Next, conductive paste 8 (made by Tatsuta Electric Wire & Cable Co.,Ltd., model number “AE1244”) is applied to the external surface of thecarrier base 7 using a spatula so that the through holes 3 are filled inwith this conductive paste 8, and after that, the carrier base 7 isreleased from the resin layer 4 so that a sheet 13 f having the throughholes 3 filled with the conductive paste 8 is gained.

In addition, the same copper foil as the one used for fabricating theabove described wiring board sheet 1 i is prepared as the metal foil 9.

Then, the sheet 13 f is placed on the surface of the wiring board sheet1 i on the side where the conductor circuit 5 has been formed so thatthe surface from which the conductive paste 8 protrudes is opposite tothe conductor circuit 5 and furthermore, the metal foil 9 is layered andplaced on the external surface side of the sheet 13 f so that the roughsurface of the metal foil 9 is opposite to the sheet 13 f and heatingmolding is carried out for 60 minutes at a heating temperature of 175°C. so that the layers are integrated.

Subsequently, the gained layered body is irradiated with a YAG laserunder the condition of 15 KHz, 1.8 W and 50 shots, and thereby, throughholes are created so as to penetrate the entirety of the layered body,and after that, desmear treatment is carried out on the inner surfacesof the through holes so that hole plating 18 having a thickness of 20 μmis formed of electroless plating and electrolytic plating. Furthermore,an etching treatment is carried out on the metal foils 9 on the externallayers on both sides so as to carry out surface layer patterning andconductor circuits 5 are formed on the external layers on both sides,and thus, a multilayer board 11 is gained.

TABLE 1 Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Embodiment 5Cresol novolac-type epoxy resin 1.2 7.0 — 1.2 — Polyfunctional bisphenol— — 7 — 7.0 A-type epoxy resin Bisphenol A-type epoxy resin 0.4 — — 0.4— Bisphenol F-type epoxy resin — 3.1 0.9 — 0.9 Phenoxy resin 0.3 0.8 10.3 1 Brominated epoxy resin 1.0 2.55 4 1.0 4 Phenolic novolac resin 1.0— — 1.0 — (curing agent) Dicyandiamide (curing agent) — 0.5 1 — 1 2E4MZ(curing accelerator) 0.1 0.05 0.1 0.1 0.1 Triphenyl phosphine 0.1 — —0.1 — (curing accelerator) Alumina 85 60 — 95 — Aluminum nitride 10 — —— 60 Boron nitride — 25 — — 25 Silica — — 85 — — Epoxy silane (couplingagent) 1 0.8 0.8 1 0.8 M208F (dispersing agent) — 0.2 0.2 — 0.2 Type ofsolvent Methyl ethyl Acetone, Methyl ethyl Methyl ethyl Methyl ethylketone dimethyl ketone, ketone ketone, formamide dimethyl dimethylformamide formamide Carrier base Rolled copper PET PET PET Glass unwovenfoil cloth Base for transcription SUS301 SUS301 SUS304 SUS304 SUS304

The details of the respective components in the table are as follows.

-   -   Cresol novolac-type epoxy resin: made by Sumitomo Chemical Co.,        Ltd., model number “ESCN195XL4”

-   Polyfunctional bisphenol A-type epoxy resin: made by Mitsui Chemical    Co., Ltd., model number “VG3101”

-   Bisphenol A-type epoxy resin: made by Yuka Shell Epoxy Co., Ltd.,    model number “EPIKOTE 828”

-   Bisphenol F-type epoxy resin: made by Toto Kasei Industry Co., Ltd.,    model number “YDF8170”

-   Phenoxy resin: made by Toto Kasei Co., Ltd., model number “YPP50”

-   Brominated epoxy resin: made by Sumitomo Chemical Co., Ltd., model    number “ESB400T”

-   Phenolic novolac resin: made by Gun Ei Chemical Industry Co., Ltd.,    model number “Tamanol 752”

-   2E4MZ: 2-methyl-4-methyl imidazole

-   Alumina: having an average grain diameter of 12 μm and a maximum    grain diameter of 50 μm

-   Aluminum nitride: having an average grain diameter of 2 μm and a    maximum grain diameter of 15 μm

-   Boron nitride: having an average grain diameter of 1.5 μm and a    maximum grain diameter of 10 μm

-   Silica: having an average grain diameter of 2 μm and a maximum grain    diameter of 10 μm

-   Epoxy silane: made by Nippon Unicar Co., Ltd., model number “A-187”

-   M208F: made by Dai-ichi Kogyo Seiyaku Co., Ltd., model number    “M208F” of which the compound name is referred to as polyoxy    alkylene alkyl ether phosphate ester mono ethanol amine salt

INDUSTRIAL APPLICABILITY

According to the manufacturing method for a wiring board sheet of thepresent invention, a base for transcription where a conductor circuithas been placed on a surface and electric components have been mountedon or printed on this conductor circuit is layered on one or twosurfaces of a resin layer in the B-stage so that the conductor circuitas well as the electric components are opposite to the resin layer andthe conductor circuit and the electric components are buried in theresin layer; and the base for transcription is released from the resinlayer and the conductor circuit is made to remain on the resin layerside so that the conductor circuit is transcribed on the resin layer ina manner where the external surface of the resin layer and the exposedsurface of the conductor circuit are in the same plane; and therefore,the surface is formed into a flat state and the electric components areplaced in the resin layer and at this time the electric components canbe placed so that no air spaces are generated around the electriccomponents due to the fluidity of the resin layer; and therefore, whenan insulation layer is formed of the cured resin layer, a wiring boardwhere electric components are placed in the insulation layer can begained; and thereby, the number of components mounted on the wiringboard can be increased where the electric components are prevented fromsticking out from the wiring board so that the miniaturization of thewiring board can be achieved, and furthermore, there is more freedom inthe wiring design due to the expansion of the areas where the electriccomponents can be mounted; in addition, the electric components areplaced within an insulation layer without the existence of air gapsaround these electric components, and therefore, no air remains aroundthe electric components, and thus, cracking of the insulation layer,damages to the electric components and the occurrence of defects such asdisconnection of wires due to the thermal expansion of air can beprevented even in the case where the wiring board receives stress due toheat; in addition, the electric components can be placed at arbitrarypositions by melting and softening the resin layer which is thenfluidized, irrespective of the number of the mounted electric componentsand irrespective of the positions of the mounted electric components; asa result, the electric components can be placed in arbitrary portionsinside the resin layer or inside the insulation layer that has beengained by curing the resin layer. Furthermore, other components can bemounted on the surfaces of the multilayered board in which componentshave been buried.

In addition to the above described manufacturing method for a wiringboard sheet, according to the manufacturing method for a wiring boardsheet of the present invention, a conductor circuit is transcribed ononly one surface of the resin layer by using a base for transcription sothat the external surface of the resin layer and the exposed surface ofthe conductor circuit are formed to be in the same plane while a metalfoil or a metal foil with resin is layered on the other surface of theresin layer so that the foil and the resin layer are integrated, andtherefore, this metal foil is placed on the outermost layer at the timeof the formation of the multilayer board, and thereby, a circuit can beformed according to a general etching manufacturing method. In addition,the reliability concerning the tension strength of the componentsmounted on the surface layer can be easily secured by utilizing a copperfoil or the like on which a roughing treatment has been carried out.

In addition to the above described manufacturing method for a wiringboard sheet, according to the manufacturing method for a wiring boardsheet of the present invention, when a conductor circuit is placed on asurface of a base for transcription and electric components are mounted,a stainless steel base is used as the base for transcription, and aplating treatment is carried out on the surface of the base fortranscription after the formation of a resistor, and thereby, aconductor circuit is placed and electric components are mounted orprinted while underfill is placed between the electric components andthe mounting surface, and therefore, active components such as ICshaving large component areas and LCR components having large capacitieswith large areas are secured and stably mounted exhibiting the effectsof increasing the connection reliability. In addition, at least eitherresistor elements or capacitor elements, which are electric components,can be formed on the base for transcription, and thereby, the electriccomponents are mounted, and therefore, it becomes possible to form verythin elements as the electric components so that the reduction in thethickness of the wiring board can be realized. In addition, the soldercan be suppressed from flowing out at the second time when the solder ismelted by applying heat again.

In addition to the above described manufacturing method for a wiringboard sheet, according to the manufacturing method for a wiring boardsheet of the present invention, a protective film is layered on one ortwo surfaces of a resin layer after a conductor circuit has beentranscribed to the resin layer and through holes are created so as topenetrate the resin layer, the conductor circuit and the protective filmwherein the through holes are filled in with conductive paste byapplying the conductive paste from the external surface side of theprotective film and after that, the protective film is released from theresin layer so that the conductive paste is formed so as to protrudeoutwards from the through holes, and therefore, the via holes forelectrically connecting the conductor circuits can be formed atarbitrary positions.

In addition, according to the manufacturing method for a wiring boardsheet of the present invention, a metal foil is layered on the surfaceof a wiring board sheet, on the side opposite to the side where theconductor circuit has been formed, which is gained according to theabove described manufacturing method for a wiring board sheet, where theconductor circuit has been formed on only one surface so that the metalfoil and the wiring board sheet are integrated or a base fortranscription where a conductor circuit has been placed on a surface islayered on the surface of the wiring board sheet, on the side oppositeto the side where the conductor circuit has been formed, which is gainedaccording to the above described manufacturing method for a wiring boardsheet, where the conductor circuit has been formed on only one surfaceso that the conductor circuit and the resin layer are opposite to eachother, and therefore, the metal foil and the conductor circuit can beformed and the via holes for electrically making connection between themetal foil and the conductor circuit and between the conductor circuitscan be formed at arbitrary positions. In addition, the conductive viaholes are compressed at the time when the metal foil or the conductorcircuit and the resin layer are layered and integrated, and therefore,the conductive resistance of the via holes can be reduced.

In addition to the above described manufacturing method for a wiringboard sheet, according to the manufacturing method for a wiring boardsheet of the present invention, a protective film is layered on one ortwo surfaces of a resin layer after a conductor circuit has beentranscribed to one or two surfaces of the resin layer and through holesare created so as to penetrate the resin layer, the conductor circuitand the protective film and hole plating is carried out on the innersurfaces of the through holes and the through holes are filled in withresin paste or conductive paste by applying the resin paste or theconductive paste on the external surface side of the protective film,and after that, the protective film is released from the resin layer,and therefore, the hole plating can provide a high stability in theconductivity of the via holes even in the case where the paths of thevia holes formed in the resin layer are elongated due to the increasedthickness of this resin layer as a result of the buried electriccomponents. Furthermore, highly stable conductivity can additionally beprovided to the via holes by means of the conductive paste.

In addition to the above described manufacturing method for a wiringboard sheet, according to the manufacturing method for a wiring boardsheet of the present invention, a stainless steel base having athickness of 50 μm to 150 μm, where a surface roughening treatment hasbeen carried out so that the degree of surface roughness, Ra, of thesurface on which the conductor circuit is formed, becomes 2 μm or lessis used as the base for transcription, and therefore, the base fortranscription can be easily released from the resin layer by strippingthe base for transcription at the time when the conductor circuit istranscribed to the wiring board sheet under fabrication, andfurthermore, the adhesiveness between the base for transcription and theconductor circuit is adjusted by means of a surface roughing treatmentso that the conductor circuit is not released from the base fortranscription in an unprepared manner, and the conductor circuit can bemade to remain on the resin layer side without fail by releasing theconductor circuit from the base for transcription at the time when thebase for transcription is released from the resin layer in order totranscribe the conductor circuit.

In addition to the above described manufacturing method for a wiringboard sheet, according to the manufacturing method for a wiring boardsheet of the present invention, the resin layer is formed of a resincomposition that contains at least one type of inorganic filler selectedfrom among silica, alumina, aluminum nitride, boron nitride, titaniumoxide, aluminum borate and magnesium oxide where the maximum graindiameter of this inorganic filler is 10 μm or less, while theseinorganic fillers can be freely used to adjust the thermal conductivity,dielectric constant, grain distribution and color tone, and therefore,the grain size can be appropriately designed in order to selectivelyexercise desired functions and the density of the fillings can be easilyincreased so that the coefficient of thermal expansion of the resinlayer or of the insulation layer formed of this resin layer is reducedand the difference in the coefficient of thermal expansion between thebuilt in components and the material forming the conductor circuits isreduced, and thereby, the occurrence of deformation such as warping canbe prevented in the case where the multilayer board is heated such asduring the manufacture of the multilayer board or the multilayer boardthat has been manufactured, receives thermal stress.

In addition to the above described manufacturing method for a wiringboard sheet, according to the manufacturing method for a wiring boardsheet of the present invention, the resin layer is formed of a resincomposition where the content of the inorganic filler is 70 wt. % to 95wt. % and which contains at least one of a coupling agent and adispersing agent, and therefore, the inorganic filler can be filled to ahigh density while the dispersion thereof is increased so that thecoefficient of thermal expansion of the resin layer or of the insulationlayer formed of this resin layer is reduced and the difference in thecoefficient of thermal expansion between the built in components and thematerial forming the conductor circuits is reduced, and thereby, theoccurrence of deformation such as warping can be prevented in the casewhere the multilayer board is heated such as during the manufacture ofthe multilayer board or the multilayer board that has been manufactured,receives thermal stress.

In addition to the above described manufacturing method for a wiringboard sheet, according to the manufacturing method for a wiring boardsheet of the present invention, the resin layer is formed of a resinsheet that is gained by impregnating an unwoven cloth with a resincomposition, which is then dried, and therefore, a very thick resinsheet from both sides of which the solvent evaporates at the time ofbeing dried can be formed in a very cost effective manner due to itsability of effectively being dried. In addition, the resin sheet made ofan unwoven cloth is stiff and is advantageous in handling due to itstenacity in the case where a sheet of a large area is handled.Furthermore, resin easily moves over the unwoven cloth following theunevenness made of the components or the like at the time of forming thelayers, and therefore, it is particularly effective in the case wherethe resin covers an area having unevenness with large steps.

In addition to the above described manufacturing method for a wiringboard sheet, according to the manufacturing method for a wiring boardsheet of the present invention, the resin layer after having been formedis maintained in the B-stage, and therefore, can be favorably used forthe manufacture of a multilayer board and at this time, two or morewiring board sheets or at least one sheet and another sheet where aconductor circuit or a metal foil is placed in the resin layer in theB-stage are collectively layered so that a multilayer board can begained. At this time, the surface is flat and a member in sheet formmade of a resin layer in the B-stage is layered on the surface, andtherefore, no deformation occurs in the portions of the insulation layerwhere the conductor circuits have been formed during the molding processhaving a highly reliable insulation in the insulation layer, and inaddition, two or more members in sheet form are collectively layered andintegrated, and therefore, it is possible to simplify the moldingprocess, saving time and effort required for a complicated process andno difference is made in the thermal histories of the conductor circuitson the respective layers at the time of molding, making the correctionbased on the contraction ratios of the conductor circuits 5 due to thedifference in the thermal histories unnecessary. In addition, conductorcircuits can be formed in arbitrary portions of the insulation layer,providing more freedom in the wiring design, and furthermore, the viaholes can be formed at arbitrary positions when a wiring board sheetwhere via holes have been formed or another sheet is used so that avia-on-via structure or a pad-on-via structure can be easily formed, andthereby, the miniaturization of the circuit and an increase in thedensity of the circuit become easy so that scale-down and reduction inthe thickness of a wiring board can be achieved and the signal paths canbe shortened.

A wiring board sheet of the present invention has been manufacturedaccording to the above described manufacturing method for a wiring boardsheet, and therefore, the surface is formed to be in a flat state andthe electric components can be placed in a resin layer where thefluidity of the resin layer prevents air spaces from being generatedaround the electric components, and therefore, a wire board whereelectric components are provided in an insulation layer can be gainedwhen the insulation layer is formed of the cured resin layer in a mannerwhere the number of components mounted on the wiring board can beincreased while miniaturization of the wiring board can be achieved byrestricting the electric components from protruding from the wiringboard. Furthermore, the area for allowing the electric components to bemounted is expanded, providing more freedom in the wiring design and theelectric components are placed in an insulation layer without theexistence of air spaces around the electric components, and therefore,no air remains around the electric components so that cracking of theinsulation layer, damages to the electric components and occurrence ofdefects, such as disconnection of wires due to the thermal expansion ofthe air can be restricted even in the case where the wiring boardreceives stress due to heat; in addition, the resin layer is melted andsoftened so as to be fluidized so that the electric components can beplaced at arbitrary positions irrelevant of the number of the mountedelectric components or irrelevant of the positions of the mountedelectric components in a manner where the electric components can beplaced in arbitrary positions inside the resin insulation layer orinside the insulation layer made of the cured resin layer withoutundergoing a complicated process. Furthermore, other components can bemounted also on the surfaces of the multilayer board where thecomponents have been buried.

According to the manufacturing method for a multilayer board of thepresent invention, two or more wiring board sheets such as the onesdescribed in the above are layered and integrated, and therefore, amultilayer board wherein electric components are placed in an insulationlayer can be gained and the number of the components mounted on themultilayer board can be increased and miniaturization of the multilayerboard can be achieved by suppressing the electric components fromprotruding from the multilayer board. Furthermore, the area where theelectric components can be mounted is expanded, providing more freedomin the wiring design, and the electric components are placed in aninsulation layer without the existence of air spaces around the electriccomponents, and therefore, no air remains around the electric componentsin a manner where cracking of the insulation layer, damages to theelectric components and the occurrence of defects such as disconnectionof wires due to the thermal expansion of the air can be restricted evenin the case where the multilayer board receives stress due to heat. Inaddition, the electric components can be placed at arbitrary positionsirrelevant of the numbers of mounted electric components or thepositions of the mounted electric components so that electric componentscan be placed in arbitrary portions inside the insulation layer withoutundergoing a complicated process. Furthermore, other components can bemounted also on the surfaces of the multilayer board in which thecomponents have been buried. In addition, members in sheet form havingflat surfaces are layered, and therefore, no deformation occurs in theportions of the insulation layer where the conductor circuits have beenformed during the molding process, providing highly reliable insulationin the insulation layer. In addition, the gained multilayer board can beformed as a multilayered wiring board that incorporates high level LCRfunctions, and can be expected to be utilized in a microelectronicfield, such as a compact high frequency module including an RF moduleand a blue tooth module.

In addition, according to the manufacturing method for a multilayerboard of the present invention, at least one wiring board sheet asdescribed above and at least one sheet having a resin layer in the Band/or C-stage where no electric components are buried inside the sheetare layered and are integrated, and therefore, a multilayer boardwherein electric components are placed in an insulation layer can begained in a manner where the number of the components mounted in themultilayer board can be increased and miniaturization of the multilayerboard can be achieved by suppressing the electric components fromprotruding from the multilayer board; furthermore, an area where theelectric components can be mounted is expanded, providing more freedomin the wiring design and the electric components are placed in theinsulation layer without the existence of air spaces around the electriccomponents, and thereby, no air remains around the electric componentsin a manner where cracking of the insulation layer, damages to theelectric components and the occurrence of defects such as disconnectionof wires due to the thermal expansion of the air can be restricted evenin the case where the multilayer board receives stress due to heat. Inaddition, the electric components can be placed at arbitrary positionsirrelevant of the numbers of mounted electric components or thepositions of the mounted electric components so that electric componentscan be placed in arbitrary portions inside the insulation layer withoutundergoing a complicated process. Furthermore, other components can bemounted also on the surfaces of the multilayer board in which thecomponents have been buried. In addition, members in sheet form havingflat surfaces are layered, and therefore, no deformation occurs in theportions of the insulation layer where the conductor circuits have beenformed during the molding process, providing highly reliable insulationin the insulation layer. In addition, the gained multilayer board can beformed as a multilayered wiring board that incorporates high level LCRfunctions, and can be expected to be utilized in a microelectronicfield, such as a compact high frequency module including an RF moduleand a blue tooth module.

In addition to the above described manufacturing method for a multilayerboard, according to the manufacturing method for a multilayer board ofthe present invention, at least one wiring board sheet as describedabove and at least one sheet having a resin layer in the B and/orC-stage where no electric components are buried inside the sheet arelayered so as to be integrated in this condition, that is to say two ormore members in sheet form are collectively layered and integrated, andtherefore, it is possible to simplify the molding process, saving timeand effort for a complicated process, and no difference is made in thethermal histories of the conductor circuits on the respective layers atthe time of molding, making the correction based on the contractionratios of the conductor circuits due to the difference in the thermalhistories unnecessary.

In addition to the above described manufacturing method for a multilayerboard, according to the manufacturing method for a multilayer board ofthe present invention, at least one wiring board sheet as describedabove is used in order to integrate multiple layers and in order tocreate via holes in accordance with a build-up manufacturing method, andtherefore, a variety of types of sheet materials can be used for thecore portion and it becomes possible to manufacture a multilayer boardhaving highly reliable connections wherein layers are formed inaccordance with a general build-up manufacturing method, vias are formedby means of laser processing, plating and the like. For example, when awiring board sheet that incorporates electric components is used as thecore portion, this sheet can be utilized as the core material so that asubstrate that incorporates components can be easily fabricated inaccordance with a build-up manufacturing method.

In addition to the above described manufacturing method for a multilayerboard, according to the manufacturing method for a multilayer board ofthe present invention, through holes are created so as to penetrate thelayered body after the layers have been integrated, and after holeplating has been placed on the inner surfaces of the through holes,these through holes are filled in with resin paste or conductive paste,and therefore, additional through holes can be created so as topenetrate the entirety of the multilayer board after the layers havebeen integrated, providing more freedom in the wiring design and a highstability in the conductivity of the through holes can be secured by theusage of both the hole plating and the conductive paste.

A multilayer board of the present invention has been manufacturedaccording to the above described manufacturing method for a multilayerboard, and therefore, a multilayer board where electric components areplaced in an insulation layer can be gained in a manner where the numberof components mounted in the multilayer board can be increased and theminiaturization of the multilayer board can be achieved by suppressingthe electric components from protruding from the multilayer board;furthermore, an area where the electric components can be mounted isexpanded, providing more freedom in the wiring design and the electriccomponents are placed in the insulation layer without the existence ofair spaces around the electric components, and thereby, no air remainsaround the electric components in a manner where cracking of theinsulation layer, damages to the electric components and the occurrenceof defects such as disconnection of wires due to the thermal expansionof the air can be restricted even in the case where the multilayer boardreceives stress due to heat. In addition, the electric components can beplaced at arbitrary positions irrelevant of the numbers of mountedelectric components or the positions of the mounted electric componentsso that electric components can be placed in arbitrary portions insidethe insulation layer without undergoing a complicated process.Furthermore, other components can be mounted also on the surfaces of themultilayer board in which the components have been buried. In addition,members in sheet form having flat surfaces are layered, and therefore,no deformation occurs in the portions of the insulation layer where theconductor circuits have been formed during the molding process,providing highly reliable insulation in the insulation layer. Inaddition, the gained multilayer board can be formed as a multilayeredwiring board that incorporates high level LCR functions, and can beexpected to be utilized in a microelectronic field, such as a compacthigh frequency module including an RF module and a blue tooth module.

1. A method for manufacturing a wiring board sheet, comprising: placinga conductor circuit on a base for transcription and mounting or formingthrough printing an electric component on the conductor circuit;layering the base and conductor circuit on an external surface of aresin layer in the B-stage so that the conductor circuit and electriccomponent are opposite to the external surface of the resin layer andthe conductor circuit and electric component are buried in the resinlayer; then releasing the base from the resin layer while permitting theconductor circuit to remain in the resin layer external surface suchthat the external surface of the resin layer and an exposed surface ofthe conductor circuit are in the same plane; then layering a protectivefilm on the external surface of the resin layer and the exposed surfaceof the conductor circuit; then creating a through hole that penetratesthe protective film, conductor circuit and resin layer; applying aconductive paste to an external side of the protective film to fill thethrough hole with the conductive paste; and then releasing theprotective film from the resin layer so that the conductive pasteprotrudes outwardly from the through hole above the plane of theexternal surface of the resin layer and the exposed surface of theconductor circuit.
 2. The method of claim 1 and further comprising:layering a second base, second conductor circuit and second electriccomponent on an opposite external surface of the resin layer so that thesecond conductor circuit and second electric component are buried in theresin layer; then releasing the second base from the resin layer whilepermitting the second conductor circuit to remain in the resin layeropposite external surface such that the opposite external surface of theresin layer and an exposed surface of the second conductor circuit arein the same plane; then layering a second protective film on theopposite external surface of the resin layer and the exposed surface ofthe second conductor circuit; the through hole penetrating the secondprotective film and second conductor circuit; and then releasing thesecond protective film from the resin layer so that the conductive pasteprotrudes outwardly from the through hole above the plane of theopposite external surface of the resin layer and the exposed surface ofthe second conductor circuit.
 3. The method of claim 1 and layering ametal foil or metal foil with resin on an opposite external surface ofthe resin layer and integrating the foil or foil with resin with theopposite external surface.
 4. The method of claim 1 wherein the base fortranscription is stainless steel and the conductor surface is placedthereon by a plating treatment after the formation of a resist on thesurface of the base.
 5. The method of claim 1 wherein the base fortranscription is stainless steel having a thickness of from 50 μm to 150μm on which a surface roughening treatment has been carried out toproduce a surface roughness R_(a) on the surface on which the conductorcircuit is placed of 2 μm or less.
 6. The method of claim 1, wherein theresin layer is formed of a resin composition that contains at least onetype of inorganic filler selected from the group consisting of silica,alumina, aluminum nitride, boron nitride, titanium oxide, aluminumborate and magnesium oxide, wherein the maximum grain diameter of saidorganic fillers is 10 μm or less.
 7. The method of claim 1, wherein theresin layer is formed of a resin composition having an organic filler ofwhich the content of the inorganic filler is from 70 wt. % to 95 wt. %and that contains at least a coupling agent or a dispersing agent. 8.The method of claim 1, wherein the resin layer is formed of a resinsheet produced by impregnating an unwoven cloth with a resin compositionwhich is then dried.
 9. The manufacturing method of claim 1, whereinafter formation of the resin layer, the resin layer is maintained in theB-stage.
 10. A method for manufacturing a wiring board sheet,comprising: placing a conductor circuit on a base for transcription andmounting or forming through printing an electric component on theconductor circuit; layering the base and conductor circuit on anexternal surface of a resin layer in the B-stage so that the conductorcircuit and electric component are opposite to the external surface ofthe resin layer and the conductor circuit and electric component areburied in the resin layer; then releasing the base from the resin layerwhile permitting the conductor circuit to remain in the resin layerexternal surface such that the external surface of the resin layer andan exposed surface of the conductor circuit are in the same plane; thenlayering a protective film on the external surface of the resin layerand the exposed surface of the conductor circuit; then creating athrough hole that penetrates the protective film, conductor circuit andresin layer; plating the inner surface of the through hole; applying aresin or conductive paste to an external side of the protective film tofill the through hole with the resin or conductive paste; and thenreleasing the protective film from the resin layer so that the resin orconductive paste protrudes outwardly from the through hole above theplane of the external surface of the resin layer and the exposed surfaceof the conductor circuit.
 11. The method of manufacturing a multi-layerboard by layering and integrating a plurality of wiring board sheetswherein each of said sheets is formed by the following method: placing aconductor circuit on a base for transcription and mounting or formingthrough printing an electric component on the conductor circuit;layering the base and conductor circuit on an external surface of aresin layer in the B-stage so that the conductor circuit and electriccomponent are opposite to the external surface of the resin layer andthe conductor circuit and electric component are buried in the resinlayer; then releasing the base from the resin layer while permitting theconductor circuit to remain in the resin layer external surface suchthat the external surface of the resin layer and an exposed surface ofthe conductor circuit are in the same plane; then layering a protectivefilm on the external surface of the resin layer and the exposed surfaceof the conductor circuit; then creating a through hole that penetratesthe protective film, conductor circuit and resin layer; applying aconductive paste to an external side of the protective film to fill thethrough hole with the conductive paste; and then releasing theprotective film from the resin layer so that the conductive pasteprotrudes outwardly from the through hole above the plane of theexternal surface of the resin layer and the exposed surface of theconductor circuit.
 12. The method of claim 11 wherein said through holeis created after the layering and integrating process and said hole isplated on its inner surface prior to filling with the conductive paste.13. The method of manufacturing a multi-layer board by layering andintegrating a plurality of wiring board sheets wherein each of saidsheets is formed by the following method: placing a conductor circuit ona base for transcription and mounting or forming through printing anelectric component on the conductor circuit; layering the base andconductor circuit on an external surface of a resin layer in the B-stageso that the conductor circuit and electric component are opposite to theexternal surface of the resin layer and the conductor circuit andelectric component are buried in the resin layer; then releasing thebase from the resin layer while permitting the conductor circuit toremain in the resin layer external surface such that the externalsurface of the resin layer and an exposed surface of the conductorcircuit are in the same plane; then layering a protective film on theexternal surface of the resin layer and the exposed surface of theconductor circuit; then creating a through hole that penetrates theprotective film, conductor circuit and resin layer; applying aconductive paste to an external side of the protective film to fill thethrough hole with the conductive paste; then releasing the protectivefilm from the resin layer so that the conductive paste protrudesoutwardly from the through hole above the plane of the external surfaceof the resin layer and the exposed surface of the conductor circuit;layering a second base, second conductor circuit and second electriccomponent on an opposite external surface of the resin layer so that thesecond conductor circuit and second electric component are buried in theresin layer; then releasing the second base from the resin layer whilepermitting the second conductor circuit to remain in the resin layeropposite external surface such that the opposite external surface of theresin layer and an exposed surface of the second conductor circuit arein the same plane; then layering a second protective film on theopposite external surface of the resin layer and the exposed surface ofthe second conductor circuit; the through hole penetrating the secondprotective film and second conductor circuit; and then releasing thesecond protective film from the resin layer so that the conductive pasteprotrudes outwardly from the through hole above the plane of theopposite external surface of the resin layer and the exposed surface ofthe second conductor circuit.
 14. A method of manufacturing a multilayerboard comprising layering and integrating a wiring board sheet and atleast one sheet having a resin layer in the B and/or C-stage and beingdevoid of an electric component buried therein, wherein said wiringboard sheet is formed by the following method: placing a conductorcircuit on a base for transcription and mounting or forming throughprinting an electric component on the conductor circuit; layering thebase and conductor circuit on an external surface of a resin layer inthe B-stage so that the conductor circuit and electric component areopposite to the external surface of the resin layer and the conductorcircuit and electric component are buried in the resin layer; thenreleasing the base from the resin layer while permitting the conductorcircuit to remain in the resin layer external surface such that theexternal surface of the resin layer and an exposed surface of theconductor circuit are in the same plane; then layering a protective filmon the external surface of the resin layer and the exposed surface ofthe conductor circuit; then creating a through hole that penetrates theprotective film, conductor circuit and resin layer; applying aconductive paste to an external side of the protective film to fill thethrough hole with the conductive paste; and then releasing theprotective film from the resin layer so that the conductive pasteprotrudes outwardly from the through hole above the plane of theexternal surface of the resin layer and the exposed surface of theconductor circuit.
 15. A method of manufacturing a multilayer boardcomprising layering and collectively molding a wiring board sheet and atleast one sheet having a resin layer in the B and/or C-stage and beingdevoid of an electric component buried therein, wherein said wiringboard sheet is formed by the following method: placing a conductorcircuit on a base for transcription and mounting or forming throughprinting an electric component on the conductor circuit; layering thebase and conductor circuit on an external surface of a resin layer inthe B-stage so that the conductor circuit and electric component areopposite to the external surface of the resin layer and the conductorcircuit and electric component are buried in the resin layer; thenreleasing the base from the resin layer while permitting the conductorcircuit to remain in the resin layer external surface such that theexternal surface of the resin layer and an exposed surface of theconductor circuit are in the same plane; then layering a protective filmon the external surface of the resin layer and the exposed surface ofthe conductor circuit; then creating a through hole that penetrates theprotective film, conductor circuit and resin layer; applying aconductive paste to an external side of the protective film to fill thethrough hole with the conductive paste; and then releasing theprotective film from the resin layer so that the conductive pasteprotrudes outwardly from the through hole above the plane of theexternal surface of the resin layer and the exposed surface of theconductor circuit.
 16. A wiring board sheet made by the followingmethod: placing a conductor circuit on a base for transcription andmounting or forming through printing an electric component on theconductor circuit; layering the base and conductor circuit on anexternal surface of a resin layer in the B-stage so that the conductorcircuit and electric component are opposite to the external surface ofthe resin layer and the conductor circuit and electric component areburied in the resin layer; then releasing the base from the resin layerwhile permitting the conductor circuit to remain in the resin layerexternal surface such that the external surface of the resin layer andan exposed surface of the conductor circuit are in the same plane; thenlayering a protective film on the external surface of the resin layerand the exposed surface of the conductor circuit; then creating athrough hole that penetrates the protective film, conductor circuit andresin layer; applying a conductive paste to an external side of theprotective film to fill the through hole with the conductive paste; andthen releasing the protective film from the resin layer so that theconductive paste protrudes outwardly from the through hole above theplane of the external surface of the resin layer and the exposed surfaceof the conductor circuit.
 17. A multilayer board made by layering andintegrating a plurality of wiring board sheets wherein each of saidsheets is made by the following method: placing a conductor circuit on abase for transcription and mounting or forming through printing anelectric component on the conductor circuit; layering the base andconductor circuit on an external surface of a resin layer in the B-stageso that the conductor circuit and electric component are opposite to theexternal surface of the resin layer and the conductor circuit andelectric component are buried in the resin layer; then releasing thebase from the resin layer while permitting the conductor circuit toremain in the resin layer external surface such that the externalsurface of the resin layer and an exposed surface of the conductorcircuit are in the same plane; then layering a protective film on theexternal surface of the resin layer and the exposed surface of theconductor circuit; then creating a through hole that penetrates theprotective film, conductor circuit and resin layer; applying aconductive paste to an external side of the protective film to fill thethrough hole with the conductive paste; and then releasing theprotective film from the resin layer so that the conductive pasteprotrudes outwardly from the through hole above the plane of theexternal surface of the resin layer and the exposed surface of theconductor circuit.
 18. A module utilized in the microelectronics fieldmade by layering and integrating a plurality of wiring board sheetswherein each of said sheets is made by the following method: placing aconductor circuit on a base for transcription and mounting or formingthrough printing an electric component on the conductor circuit;layering the base and conductor circuit on an external surface of aresin layer in the B-stage so that the conductor circuit and electriccomponent are opposite to the external surface of the resin layer andthe conductor circuit and electric component are buried in the resinlayer; then releasing the base from the resin layer while permitting theconductor circuit to remain in the resin layer external surface suchthat the external surface of the resin layer and an exposed surface ofthe conductor circuit are in the same plane; then layering a protectivefilm on the external surface of the resin layer and the exposed surfaceof the conductor circuit; then creating a through hole that penetratesthe protective film, conductor circuit and resin layer; applying aconductive paste to an external side of the protective film to fill thethrough hole with the conductive paste; and then releasing theprotective film from the resin layer so that the conductive pasteprotrudes outwardly from the through hole above the plane of theexternal surface of the resin layer and the exposed surface of theconductor circuit.